U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009–5202

In cooperation with the National Atlas of the United States of America®

Production of a National 1:1,000,000-Scale Hydrography 

Dataset for the United States—Feature Selection, 

Simplification, and Refinement
Front cover: 1:1,000,000-scale continental United States streams.
Production of a National 1:1,000,000-

Scale Hydrography Dataset for the United 

States—Feature Selection, Simplification, 

and Refinement

By Robin H. Gary, Zachary D. Wilson, Christy-Ann M. Archuleta, Florence E. 

Thompson, and Joseph Vrabel

In cooperation with the National Atlas of the United States of America®

Scientific Investigations Report 2009–5202

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Gary, R.H., Wilson, Z.D., Archuleta, C.M., Thompson, F.E., and Vrabel, Joseph, 2009, Production of a national 

1:1,000,000-scale hydrography dataset for the United States—Feature selection, simplification, and refinement: U.S. 

Geological Survey Scientific Investigations Report 2009–5202, 22 p.
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Purpose and Scope .............................................................................................................................1

Acknowledgments ...............................................................................................................................2

Feature Selection ..........................................................................................................................................2

Datasets .................................................................................................................................................2

Streams ..................................................................................................................................................6

Methods Evaluated .....................................................................................................................6

Utility Network Analyst .....................................................................................................6

Geographic Names Information System Names Hierarchy .......................................6

Hydrologic Derivatives ......................................................................................................7

NHDPlus Thinner Code .....................................................................................................7

Established Production Method ...............................................................................................7

Headwater Selection ........................................................................................................7

Downstream Trace Algorithm ..........................................................................................9

Manual Editing ...................................................................................................................9

Quality Assurance ...........................................................................................................10

Waterbodies .......................................................................................................................................10

Methods Evaluated ...................................................................................................................10

Established Production Method .............................................................................................10

Simplification ...............................................................................................................................................10

Refinement ...................................................................................................................................................11

Streams ................................................................................................................................................11

Stream-Density Analysis .........................................................................................................13

Stream-Density Adjustment ....................................................................................................13

Evaluation of Stream-Density Adjustment ............................................................................15

Waterbodies .......................................................................................................................................17

Feature Geometry Modifications ...........................................................................................18

Name Updates ...........................................................................................................................18

Summary .......................................................................................................................................................19

Selected References ..................................................................................................................................19

Glossary ........................................................................................................................................................22

Figures

1. International Map of the World (IMW) map sheet index for the continental United 

States .............................................................................................................................................3

2. International Map of the World (IMW) map sheet index for (A) Alaska and

(B) Hawaii ......................................................................................................................................4

3. Diagram showing general processing steps required to select National 

Hydrography Dataset stream features for inclusion in the 1:1,000,000-scale 

streams dataset ...........................................................................................................................8
iv

4–9. Maps showing: 

4. Reaches symbolized using the feature-level metadata that document why 

individual reaches were included in the 1:1,000,000-scale streams dataset ...........9

5. (A) Original National Hydrography Dataset 1:100,000-scale waterbody 

polygon with 2,297 vertices and (B) simplified 1:1,000,000-scale waterbody 

polygon with 1,032 vertices .............................................................................................11

6. Preliminary 1:1,000,000-scale streams dataset showing stream-density 

disparity along adjoining boundaries of International Map of the World map 

sheets, continental United States ..................................................................................12

7. Example of stream-density disparity along International Map of the World 

(IMW) map sheet boundary (A) before and (B) after refinement of the 

1:1,000,000-scale streams dataset .................................................................................13

8. Density discrepancy polygons (based on intersection of International Map 

of the World map sheet boundaries and National Hydrography Dataset 

subregion boundaries) symbolized by the ratio of density in the 1:1,000,000-

scale (1:1M) stream network to density in the National Atlas 1:2,000,000-scale 

(1:2M) stream network (A) before and (B) after refinement of the 1:1M 

streams dataset ................................................................................................................14

9. Density-adjusted 1:1,000,000-scale streams dataset showing less density 

disparity (compared to that shown in fig. 6) along adjoining boundaries of 

International Map of the World map sheets, continental United States .................16

10. Area-weighted histograms and fitted normal distributions of unadjusted and 

adjusted stream-density ratios ................................................................................................17

11. Maps showing example of (A) unmodified waterbodies and (B) corresponding 

modified waterbodies ...............................................................................................................18

Tables

1. Codes used to document reach selection for the 1:1,000,000-scale streams dataset .....8

2. Weighting factors used to adjust National Atlas 1:2,000,000-scale streams features

to allow for comparison to 1:1,000,000-scale streams ............................................................15

3. Summary statistics of unadjusted and adjusted stream-density ratios ...........................17

Conversion Factors, Datum, and Abbreviations

Inch/Pound to SI

Multiply By To obtain

Length

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)
v

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Abbreviations

AGS American Geographical Society

AMS Army Map Service

DEM Digital elevation model

DLG Digital line graph

EDNA Elevation Derivatives for National Applications

GNIS Geographic Names Information System

IMW International Map of the World

INEGI Instituto Nacional de Estadística, Geografía e Informática (Mexico’s National

Institute for Statistics, Geography, and Informatics)

NED National Elevation Dataset

NGA National Geospatial-Intelligence Agency

NHD National Hydrography Dataset

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VAA Value-added attribute

VMAP0 Vector Map Level 0 
Blank Page
Production of a National 1:1,000,000-Scale Hydrography 

Dataset for the United States—Feature Selection, 

Simplification, and Refinement

By Robin H. Gary, Zachary D. Wilson, Christy-Ann M. Archuleta, Florence E. Thompson, and Joseph Vrabel

Abstract

During 2006–09, the U.S. Geological Survey, in cooperation with the National Atlas of the United States®, produced 

a 1:1,000,000-scale (1:1M) hydrography dataset comprising 

streams and waterbodies for the entire United States, including 

Puerto Rico and the U.S. Virgin Islands, for inclusion in the 

recompiled National Atlas. This report documents the methods 

used to select, simplify, and refine features in the 1:100,000-

scale (1:100K) (1:63,360-scale in Alaska) National Hydrography Dataset to create the national 1:1M hydrography dataset. 

Custom tools and semi-automated processes were created to 

facilitate generalization of the 1:100K National Hydrography 

Dataset (1:63,360-scale in Alaska) to 1:1M on the basis of 

existing small-scale hydrography datasets. The first step in 

creating the new 1:1M dataset was to address feature selection and optimal data density in the streams network. Several 

existing methods were evaluated. The production method that 

was established for selecting features for inclusion in the 1:1M 

dataset uses a combination of the existing attributes and network in the National Hydrography Dataset and several of the 

concepts from the methods evaluated. The process for creating 

the 1:1M waterbodies dataset required a similar approach to 

that used for the streams dataset. Geometric simplification of 

features was the next step. Stream reaches and waterbodies 

indicated in the feature selection process were exported as new 

feature classes and then simplified using a geographic information system tool. The final step was refinement of the 1:1M 

streams and waterbodies. Refinement was done through the 

use of additional geographic information system tools.

Introduction

A 1:1,000,000-scale (1:1M) nationwide hydrography 

dataset is critical to meeting the evolving needs of the National 

Atlas of the United States® (National Atlas of the United 

States, 2008). Within the scope of the National Atlas, preparation, integration, and maintenance of national, small-scale 

(relatively large area) cartographic frameworks are essential 

to promoting collaboration, research, and cost savings across 

the spectrum of Federal geospatial and geostatistical data 

users and producers. The National Atlas fills the need for 

small-scale cartographic frameworks by collaborating with 

mapping agencies in Mexico and Canada on the 1:10,000,000-

scale (1:10M) North American continental framework and by 

producing and maintaining the 1:2,000,000-scale (1:2M), and 

now the 1:1M framework datasets of the United States. Formal 

working relationships between the U.S. Geological Survey 

(USGS) and Instituto Nacional de Estadística, Geografía e 

Informática (INEGI, Mexico’s National Institute for Statistics, 

Geography, and Informatics) and between the USGS and the 

Natural Resources Canada Earth Sciences Sector enable the 

three organizations to collaborate on the production and maintenance of the North American Atlas 1:10M datasets. 

During 2006–09, as part of an effort to recompile 

National Atlas 1:2M data layers at 1:1M and fulfill the goal 

of the Global Mapping Initiative1, the USGS, in cooperation with the National Atlas of the United States, produced 

a 1:1M hydrography dataset comprising streams and waterbodies (referred to as water courses and inland water in the 

Global Map). The focus of this production effort was to create 

datasets of 1:1M streams and waterbodies, with appropriate 

stream density, using a method for selecting features from 

the National Hydrography Dataset (NHD) (U.S. Geological Survey, 2008) that would be consistent across the entire 

United States and also would maintain network connectivity. 

Additionally, the vast cartographic knowledge embedded in 

the National Atlas and other datasets was to be retained. 

Purpose and Scope

This report documents the methods used to select, 

simplify, and refine features in the 1:100,000-scale (1:100K) 

(1:63,360-scale in Alaska) NHD to create a national 1:1M 

hydrography dataset for inclusion in the recompiled National 

Atlas of the United States. The 1:1M hydrography dataset 

encompasses the entire United States, including Puerto Rico 

and the U.S. Virgin Islands. Using small-scale, ancillary 

datasets for reference, the features included in the 1:1M 

1

 The goal of the Global Mapping Initiative is to develop a global coverage 

of 1:1M geographic datasets that include elevation, vegetation, land cover, 

land use, transportation, drainage systems, boundaries, and population centers. 

These datasets will facilitate environmental monitoring at a global scale.
2 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

hydrography dataset were selected using custom tools and 

semi-automated processes that leveraged the geometric 

network and detailed attributes available in the NHD. The 

features in the 1:1M streams and waterbodies datasets were 

simplified to create less complex features as well as to reduce 

storage requirements. Streams were refined to equalize areas 

of stream-density disparity and remove density artifacts 

(sometimes called map faults). Waterbodies were refined to 

adjust feature geometry and name attributes affected by different source maps.

Acknowledgments

The authors thank Anna Regan and Andrew Murray 

(Natural Resources Canada, Ottawa, Ontario, Canada) and 

José Luis Ornelas (INEGI, Aguascalientes, Aguascalientes, 

Mexico) for their work on harmonizing data along international boundaries, and Taro Ubukawa (Geographic Survey 

Institute of Japan, International Steering Committee for Global 

Mapping Secretariat) for his help distributing the Global Mapping Initiative data.

Feature Selection

Datasets

Several readily available, small-scale, nationwide 

hydrographic datasets exist, although none of these ancillary datasets singularly fills the needs of the National Atlas 

recompilation effort or the Global Mapping initiative specifications. National Atlas maintains 1:2M datasets of streams and 

waterbodies of the United States (National Atlas of the United 

States, 2006). The National Geospatial-Intelligence Agency 

(NGA) distributes the Vector Map Level 0 (VMAP0) datasets 

compiled at 1:1M (National Geospatial-Intelligence Agency, 

1998). A variety of national mapping agencies produced 

paper map sheets at 1:1M for the International Map of the 

World (IMW) series (available at the USGS Library, Reston, 

Va.). The USGS Elevation Derivatives for National Applications (EDNA) dataset (U.S. Geological Survey, 2005a) is a 

multi-layered, 30-meter-resolution synthetic stream network 

database derived from the National Elevation Dataset (NED) 

(U.S. Geological Survey, 2006a) that includes hydrologic 

derivatives. Hydrologic derivatives are hydrologic characteristics of the land surface that have been calculated from a digital 

elevation model (DEM). The collaborative NHD program, 

led by the USGS, also provides large-scale (1:63,360) to 

intermediate-scale (1:100,000) surface-water data.

The features of the 1:2M datasets of streams and waterbodies of the United States were originally digitized by the 

USGS from the 21 general reference maps contained in “The 

National Atlas of the United States of America” published in 

hardcopy (U.S. Geological Survey, 1970). The 1:2M Digital 

Line Graph (DLG) data were merged into a single national 

water features dataset; then names, feature types, and geometry were updated using 1:250,000 (1:250K), 1:100K, and 

1:24,000 (1:24K) USGS topographic maps. To avoid losing the cartographic information in the National Atlas 1:2M 

streams and waterbodies datasets, the 1:2M data were used as 

the highest priority source for feature selection for inclusion 

in the new 1:1M datasets. Features in the National Atlas 1:2M 

datasets are represented in the 1:1M datasets.

VMAP0 is an updated and enhanced version of the 

National Imagery and Mapping Agency (now NGA) Digital 

Chart of the World. The VMAP0 hydrographic dataset at 1:1M 

is based on source data collected from 1972 through 1992. The 

original data source for VMAP0 was the 1:1M Operational 

Navigational Chart series that was produced by the military 

mapping agencies of Australia, Canada, the United Kingdom, and the United States. VMAP0 data were used as the 

initial vector datasets in the Global Mapping Initiative so that 

national mapping agencies could verify and improve the existing data (Pearson and others, 2006). 

The IMW series predates the Global Mapping Initiative 

as the first attempt to construct maps based on a common 

scale and universally accepted conventions. Maps from the 

IMW series were produced by numerous organizations from 

the 1910s to the 1970s and distributed as paper maps. A set of 

general standards guided extent, projection, content, and symbology. However, as more IMW maps were produced, maintaining consistency became increasingly difficult (Heffernan, 

2002; Pearson and others, 2006). The 69 IMW maps that cover 

the continental United States, Alaska, and Hawaii were produced between 1934 and 1978 by the USGS, Army Map Service (AMS), American Geographical Society (AGS), and the 

Canada Department of Energy, Mines, and Resources (figs. 1, 

2) (see “Selected References”). Each map contains similar 

content, but each varies in detail because of differences in 

source data used to compile the map and because of variance 

in standards used by the compiling agencies. The hardcopy 

IMW maps at the USGS Library in Reston, Va., were scanned 

and orthorectified using a minimum of 10 control points and a 

third-order polynomial transformation (ESRI®, 2008c).

The USGS distributes and maintains the EDNA dataset, 

the synthetic stream network derived from the NED. The NED 

is a seamless DEM composed of the highest-resolution and 

best-quality elevation data available for the Nation. The synthetic stream network is constructed by computing flow accumulation and flow direction, then deriving flow paths. Because 

the synthetic stream network depends on the resolution of the 

NED, scale is difficult to define for the derivative datasets; 

however, several derivatives can help indicate stream order. 

For example, one of the elevation derivative datasets estimates 

mean annual streamflow for the synthetic stream network by 

using catchment area and annual precipitation data.

The NHD is a nationwide surface-water dataset that 

includes networked flowlines (digital spatial data representing streams or canals) with flow direction available 

for intermediate (1:100K) to large (1:63,360) scales. The 
Monterrey

AGS, 1937

None given

Florida Keys

AMS, 1959

1:250k

Sonora

AGS, 1937

None given

Chihuahua

AGS, 1934

None given

Austin

USGS, 1945

Other large scale

White Lake

AMS, 1956

1:250k

Mobile

AMS, 1959

1:250k

Jacksonville

AMS, 1956

1:250k

Point Conception

AMS, 1959

1:250k

Los Angeles

USGS, 1947

Other large scale Gila River AMS, 1959

1:250k

Santa Fe

AMS, 1955

1:250k

Dallas

AMS, 1959

1:250k

Vicksburg

AMS, 1956

1:250k

Lookout Mountain

USGS, 1968

1:500k, 1:250k

Savannah

USGS, 1978

Other large scale

Hatteras

AMS, 1955

1:250k

San Francisco Bay

AMS, 1959

1:250k Mount Whitney USGS, 1966

Other large scale Grand Canyon

AMS, 1959

1:250k

Pikes Peak

USGS, 1966

Other large scale

Wichita

AMS, 1955

1:250k

Ozark Plateau

USGS, 1971

1:500k, 1:250k

Louisville

AMS, 1959

1:250,000

Blue Ridge

USGS, 1972

1:500k, 1:250k

Chesapeake Bay

AMS, 1955

1:250k

Mount Shasta

AMS, 1959

1:250k Owyhee River AMS, 1959

1:250k

Great Salt Lake

AMS, 1955

1:250k

Cheyenne

AMS, 1955

1:250k

Platte River

AMS, 1959

1:250k

Des MoinesUSGS, 1970

1:500k, 1:250k

Chicago

USGS, 1973

1:500k, 1:250k

Lake Erie

USGS, 1974

1:500k, 1:250k

Hudson River

USGS, 1974

1:500k, 1:250k

Boston

AMS, 1955

1:250k

Cascade Range

USGS, 1945

Other large scale Snake River AMS, 1960

1:250k

Yellowstone

AMS, 1955

1:250k

Big Horn Mountains

AMS, 1955

1:250k

Dakotas

AMS, 1955

1:250k

Minneapolis

AMS, 1955

1:250k

Lake Superior

USGS, 1966

Other large scale

Sudbury

Canada, 1969

1:250,000

Ottawa

Canada, 1974

Other

Quebec

USGS, 1968

1:500k

Vancouver

Canada, 1967

1:250k Kootenay Lake

Canada, 1967

Other large scale

Lethbridge

Canada, 1970

Other large scale

Regina

Canada, 1967

Other large scale

Winnipeg

Canada, 1967

Other large scale

Lake Of The Woods

Canada, 1967

Other large scale

Lake Nipigon

Canada, 1969

1:250k

AMS

AGS

USGS

Canada

70° 80° 90° 100° 110° 120° 130°

40°30°

0 600 1,200 MILES Projection: Albers equal area Central Meridian: -96

Standard Parallel 1: 29.5Standard Parallel 2: 45.5Latitude of Origin: 23Linear Unit: Meter

EXPLANATION

Army Map ServiceAmerican Geographical SocietyU.S. Geological SurveyCanada Department of Energy,Mines, and Resources 

Feature Selection 3Figure 1. International Map of the World (IMW) map sheet index for the continental United States.
Cold Bay

USGS, 1971

Other large scale

Prince Rupert

Canada, 1968

Other large scale

Bristol Bay

AMS, 1956

1:250k

Kodiak

AMS, 1956

1:250k

Sitka

AMS, 1956

Other large scale

Dease Lake

Canada, 1969

Other large scale

Bethel

AMS, 1956

1:250k

Anchorage

AMS, 1956

1:250k

Whitehorse

AMS, 1956

1:250k

Nome

AMS, 1956

1:250k

Fairbanks

AMS, 1956

Other large scale

Peel River

Canada, 1975

Other large scale

Barrow

AMS, 1956

1:250k

Umiat

AMS, 1956

1:250k

Mackenzie Bay

AMS, 1956

Other large scale

110° 120° 130° 140° 150° 160° 170° 180° 170° 160° 150°

60°50°

0 600 1,200 MILES Projection: Albers equal area

Central Meridian: -154Standard Parallel 1: 55Standard Parallel 2: 65Latitude of Origin: 50Linear Unit: Meter

(A)

AMS

USGS

Canada

EXPLANATION

Army Map ServiceU.S. Geological SurveyCanada Department of Energy,Mines, and Resources 

4 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

Figure 2. International Map of the World (IMW) map sheet index for (A) Alaska and (B) Hawaii. 
USGS

EXPLANATION

U.S. Geological Survey

Hawaii

USGS, 1971

Other large scale

150° 160°

20°

0 100 200 MILES Projection: Albers equal area

Central Meridian: -157Standard Parallel 1: 8Standard Parallel 2: 18Latitude of Origin: 3Linear Unit: Meter

(B)

Feature Selection 5Figure 2. Continued.
6 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

intermediate-scale dataset for the continental United States, 

Hawaii, Puerto Rico, and the U.S. Virgin Islands (U.S. Geological Survey, 2006b) and the large-scale dataset for Alaska 

(U.S. Geological Survey, 2006c) were used as base data to 

compile the 1:1M hydrography dataset. To facilitate discussion 

in this report, the 1:100K and 1:63,360-scale datasets used to 

compile the 1:1M hydrography dataset are referred to as the 

NHD. The NHD contains several feature classes; the flowline and waterbodies feature classes were used as the source 

data to create the 1:1M streams and waterbodies datasets, 

respectively. The NHD is based on the DLG hydrography 

data that were digitized from USGS topographic maps. The 

DLG hydrography data were integrated with information from 

the U.S. Environmental Protection Agency (USEPA) Reach 

File Version 3 (U.S. Environmental Protection Agency, 1994) 

and then structured into a geometric network to allow for 

flow analysis. Reach codes were transferred from the USEPA 

Reach File Version 3 to help identify reaches (segments) in the 

flowline dataset in hydrologic analysis. The flowline attributes 

include reach codes, feature type, flow direction, Geographic 

Names Information System (GNIS) (U.S. Geological Survey, 

2007) name, and length in kilometers. Datasets are available in 

ESRI personal geodatabase format by subregion, also known 

as 4-digit hydrologic unit codes. Two-hundred twenty-two 

subregional personal geodatabases cover the 21 regions in the 

continental United States, Alaska, Hawaii, Puerto Rico, and 

the U.S. Virgin Islands. The NHD is an ideal source dataset 

from which to derive the smaller-scale (1:1M) dataset because 

of the functionality of the geometric network and the wealth of 

feature-level attributes.

None of these sources individually provides the detail 

and accuracy needed to fulfill the requirements of the National 

Atlas recompilation effort or the Global Mapping Initiative. 

However, the existing small-scale datasets combine to form an 

appropriate indicator of stream network density. The accuracy, detail, and connectivity available in the NHD provide 

an appropriate and reliable base for the creation of a 1:1M 

hydrographic dataset. The NHD data model can be generalized 

by referencing ancillary small-scale data that cover the United 

States and its territories. 

Streams

The first step in creating the new 1:1M dataset was to 

address feature selection and optimal data density in the 

streams network. The resources necessary for selecting features from the 222 subregional personal geodatabases of the 

NHD based on manual editing would have been prohibitive; 

thus the necessity of developing custom tools and semiautomated (partially software driven, partially manual editing) 

processes. Programmatically automated methods for stream 

selection and delineation have been developed by others, 

including those described by NHDPlus (U.S. Environmental 

Protection Agency and U.S. Geological Survey, 2008); EDNA 

(U.S. Geological Survey, 2005a); and Stanislawski and others 

(2005). 

During a prototyping phase, several methods of feature 

selection were evaluated. The features selected or delineated 

using previously developed semi-automated methods were 

either insufficiently consistent at 1:1M or the methods were 

too data- and time-intensive to meet production needs. The 

production method that was established combined the most 

effective aspects of the evaluated methods to facilitate production on a national scale and to minimize the need for postselection manual quality assurance.

Methods Evaluated

Utility Network Analyst

The ArcGIS Utility Network AnalystTM (ESRI, 2008a) 

allows the user to trace downstream on any dataset that 

contains a geometric network. The NHD geodatabases have 

a built-in geometric network that stores the directionality of 

each line feature within a feature class as well as the relation 

of the feature to flow through the network. By placing a flag 

on a headwater reach, flow can be traced downstream to the 

outlet of the network. The results of the trace can be converted 

to a selection of features, the attributes of which can then 

be updated. In test cases, streams for the 1:1M dataset were 

selected using the trace downstream available through the Utility Network Analyst. In areas with divergent streamflow and 

areas with braided streams, segments in all stream paths were 

selected instead of just the segments that composed the main 

flow path. The NHD geometric network greatly increases analysis capabilities, without which the production of the 1:1M 

dataset would have taken much longer. However, the Utility 

Network Analyst tracing capabilities were insufficient to meet 

production needs.

Geographic Names Information System Names Hierarchy

NHD streams have a name attribute that is populated 

by the official geographic name registered in the GNIS. 

The GNIS Names Hierarchy method used the number of 

stream segments with the same name, as indicated by the 

GNIS attribute, to determine whether to include them in the 

1:1M dataset. This counting procedure aimed to establish a 

hierarchy such that small streams with only one or two named 

segments were not selected for inclusion in the 1:1M dataset. 

A relative threshold value for the number of stream segments 

with a particular GNIS name was estimated by comparing 

density to ancillary maps compiled at 1:1M; however, this estimation technique limited repeatability because the threshold 

value is subjective. Results of the selection procedure contained breaks in network connectivity caused by missing 

GNIS name attributes. Additionally, the resulting stream density from this selection procedure was inconsistent between 

datasets because of the variability of GNIS-name attribute 

density across the country. For example, more NHD streams 

might have GNIS name attributes in and near urban areas, 

and streams in rural areas might have fewer GNIS names. 
Feature Selection 7

Resulting stream density also might be inconsistent because 

more complicated stream networks with smaller named segments could be weighted more heavily than less complicated 

stream networks. Even if stream names were weighted by 

length instead of number of segments, the GNIS name attributes in NHD were not extensive enough to make name-hierarchy analysis feasible as a stand-alone selection procedure. 

However, the names were an important part of the production 

method that was established for selecting streams for inclusion in the 1:1M dataset.

Hydrologic Derivatives

Hydrologic derivatives are hydrologic characteristics of 

the land surface that have been calculated from a DEM. One 

important hydrologic derivative is flow accumulation, which 

is calculated by summing the number of cells that flow into 

each cell. The value recorded for a cell represents the total 

number of cells in the DEM that contribute flow to that cell. 

Flow-accumulation values can indicate the relative hydrologic 

importance of a cell in a watershed. A cell with high flowaccumulation value might indicate that the cell corresponds 

spatially to a feature in the NHD that should be included 

in the 1:1M dataset. Calculation of hydrologic derivatives, 

including flow accumulation, can be time- and data-intensive. 

Production benefited greatly from the hydrologic derivatives 

in the EDNA dataset that were calculated from the 30-meterresolution NED. 

Because flow-accumulation values can indicate the 

relative importance of a stream within a watershed, the 

NHD and EDNA flow-accumulation values were analyzed 

to establish a relation between the two datasets. Buffers of 

various sizes were created for all NHD streams and then 

used to extract statistics from the flow-accumulation raster 

data. The statistical profile of each reach was then used 

to rank the streams and determine whether a stream should 

be included in the 1:1M dataset. Results of this method 

were then compared to the National Atlas 1:2M, VMAP0 

1:1M, and IMW 1:1M datasets. This approach was successful 

in selecting reaches that correlated with the 1:1M ancillary 

datasets in the middle parts of watersheds but was less 

successful in selecting important headwater reaches and 

reaches in areas with low topographic relief. The EDNA 

flow-accumulation raster data alone were insufficient for 

determining which streams should be included in the 1:1M 

dataset; however, flow accumulation became an important 

factor either for selecting headwater reaches when the other 

ancillary datasets were ambiguous about which headwater 

reach was most important or for determining the preferred 

downstream path in cases where there were multiple downstream reaches.

NHDPlus Thinner Code

The USEPA, USGS, and Horizon Systems Corporation developed NHDPlus, a networked hydrographic 

dataset with value-added attributes (VAAs) based on the 

1:100K NHD. Among the VAAs is a Thinner Code attribute, 

which is designed to allow the user to progressively thin 

the representation of the hydrographic network by selecting 

among seven values (0–6). If values 0–6 are represented in the 

network, all reaches will be present. Starting with the Thinner 

Code value of 6, the network can be thinned by eliminating 

more Thinner Code values from the cartographic representation. Here, the goal was to select reaches to represent a 1:1M 

network; however, the NHDPlus Thinner Code values were 

not consistent enough across the United States to be used as 

the method for feature selection. Furthermore, the NHDPlus

documentation advises that Thinner Codes “are designed to 

be used for improving the performance of Web pages” and 

“they should not be used for stream classification or analysis” 

(U.S. Environmental Protection Agency and U.S. Geological 

Survey, 2008, p. 67). Thus the existing Thinner Code attribute 

was judged inadequate for feature selection.

Established Production Method

The production method that was established for selecting 

streams for inclusion in the 1:1M dataset uses a combination 

of the existing attributes and network in the NHD and several 

of the concepts from the methods evaluated. Headwaters 

were selected on the basis of published small-scale datasets, 

a downstream trace algorithm used the existing network in 

the NHD to select the downstream reaches, and then selection decisions that could not be automatically calculated 

were edited manually (fig. 3). In cases where streams are 

divergent or braided, the downstream trace algorithm selected 

reaches that form a preferred path among the available paths 

for accurate representation of streams at 1:1M. All decisions to include a reach in the final 1:1M dataset, regardless 

of whether they were made manually or automatically, were 

documented at the feature level by a reason code (table 1). 

The production method for stream and waterbody selection 

thus relied on hierarchical rules for feature selection and 

was implemented using automated and manual methods that 

reduced human error, increased repeatability, and facilitated 

feature-level documentation. 

Headwater Selection

Headwater reaches were selected manually on the 

basis of whether the stream was represented in the National 

Atlas, VMAP0, and IMW hydrography datasets, which 

served as primary indicators of 1:1M stream density. For 

example, if a headwater reach in NHD coincided spatially 

with a headwater reach in the National Atlas, then that 

NHD headwater reach was attributed for inclusion in the 

1:1M dataset. Occasionally, either National Atlas, VMAP0, 

or IMW data did not indicate a particular headwater, resulting in more than one headwater reach that could be included 

in the 1:1M dataset. In these cases, the NHD headwater reach 

with a name attribute present was attributed for inclusion in 

the 1:1M dataset. If no name attributes were present among 
8 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

Figure 3. General processing steps required to select National Hydrography Dataset stream features for inclusion in the 1:1,000,000-

scale streams dataset. 

Table 1. Codes used to document reach selection for the 1:1,000,000-scale streams dataset. 

[1:1M, 1:1,000,000-scale; HS, headwater selection; VMAP0, Vector Map Level 0; EDNA, Elevation Derivatives for National 

Applications; ME, manual editing; DT, downstream trace; GNIS_ID, Geographic Names Information System identification 

number; IMW, International Map of the World]

Reason Description Processing Number of features

0 Not a 1:1M stream (default value) Preprocessing 0

1 National Atlas HS 7,772

2 VMAP0 HS 9,591

3 National Atlas and VMAP0 HS 8,916

4 National Atlas and EDNA HS 250

5 VMAP0 and EDNA HS 254

6 National Atlas, VMAP0, and EDNA HS 246

7 EDNA ME 877

8 Orthoimagery ME 1,910

9 Only downstream reach DT 952,087

10 GNIS_ID equivalent to upstream reach DT 78,893

11 Only downstream reach with GNIS_ID DT 359

12 Only downstream reach classified as stream DT 1,343

13 Only downstream reach with flow direction DT 1,776

14 IMW HS 26,324

15 Digital topographic maps ME 2,050

18 Shortest segment DT 11,712

99 Manually excluded ME 0

Process model for generalizing 

the National Hydrography 

Dataset to 1:1,000,000-scale

National 

Hydrography 

Dataset

Preliminary

1:1M Dataset

Headwater Selection

Headwater reaches selected from NHD 

using National Atlas, VMAP0, and IMW. 

Ambiguous cases decided by EDNA or 

orthoimagery.

Reason codes 1, 2, 3, 4, 5, 6, 14 (table 1)

Downstream Trace

Starting at selected headwaters, algorithm traces downstream to find most 

important path on the basis of number of 

downstream reaches, stream name, flow 

direction, feature type, and feature 

length. 

Reason codes 9, 10, 11, 12, 13, 18 (table 1)

Manual Editing

Any decisions not made by the 

algorithm are reviewed manually using orthoimagery or 

EDNA. After manual edits, the 

dataset is entered into the 

downstream trace again. 

Reason code 7, 8, 15 (table 1)

NHD, National Hydrography Dataset

VMAP0, Vector Map Level 0

IMW, International Map of the World

EDNA, Elevation Derivatives for 

National Applications
95° 94°55' 94°50' 94°45' 94°40' 94°35' 94°30' 94°25' 94°20'

31°15'

31°10'

31°5'

31°

0 2 4 6 Miles

Projection: Albers equal area

Central Meridian: -96

Standard Parallel 1: 29.5

Standard Parallel 2: 45.5

Latitude of Origin: 23

Linear Unit: Meter

Location map

EXPLANATION

Reason code and description (see table 1)

0 - Not a 1:1,000,000 stream (default value)

1 - National Atlas

2 - Vector Map Level 0

9 - Only downstream reach

10 - Geographic Names Information System

identification number

13 - Only downstream reach with flow direction

14 - International Map of the World

Feature Selection 9

the possible headwater reaches, then the USGS EDNA data 

and digital orthoimagery were used to select the appropriate 

headwater reach. After all headwater reaches were attributed, 

a downstream trace tool was used to update attributes throughout the rest of the stream network.

Downstream Trace Algorithm

The downstream trace algorithm used was written in 

Visual Basic for Applications using ArcObjects (ESRI, 2006) 

and implemented as an easy-to-use tool within the ArcMapTM 

(ESRI, 2007) environment. The algorithm considers flow 

direction, number of adjacent downstream reaches, stream 

names, and feature type (for example, stream, canal, or artificial path) to extract preliminary 1:1M flow paths from the 

NHD (fig. 4) for inclusion in the 1:1M dataset. As the tool 

traces downstream, if there is only one downstream reach, it 

is included in the 1:1M dataset; the next downstream reach 

is analyzed in the same manner. When there is more than 

one downstream reach, the tool references a set of criteria to 

decide which of the downstream reaches should be included 

in the 1:1M dataset. Priority is given to officially named segments, segments coded as streams, and segments with flow 

direction, respectively. Once the preferred downstream reach 

is determined, the tool examines the next downstream reach in 

the same manner.

Manual Editing

If the downstream reach does not meet any of the selection criteria, the downstream trace algorithm stops processing to allow the analyst to select the appropriate downstream 

reach on the basis of digital orthoimagery, georeferenced 

topographic maps, or the EDNA dataset. After all reaches 

are updated, the dataset is then reevaluated by the algorithm 

to continue tracing downstream. The extent to which manual 

editing was required depended on the characteristics of the 

NHD in a particular subregion. Subregions with extensive 

Figure 4. Reaches symbolized using the feature-level metadata that document why individual reaches were included in the 

1:1,000,000-scale streams dataset.
10 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

GNIS names, for example, were less likely to need manual 

editing. 

Quality Assurance

After all reaches were selected, the proposed 1:1M 

network was examined for connectivity. Headwater selections 

were confirmed independently by another analyst. Hydrologic 

connectivity was checked visually and by tracing upstream 

on the network to identify reaches that needed to be added 

manually. Any gaps in the network were closed using the same 

method of feature selection described above in the “Established Production Method” section.

Waterbodies

The process for creating the 1:1M waterbodies dataset 

required a similar approach to that used for the 1:1M streams 

dataset. First, the 1:2M content represented in the National 

Atlas needed to be preserved in the new 1:1M dataset. Second, 

additional waterbodies needed to be selected from the NHD to 

represent 1:1M requirements.

Methods Evaluated

The NHD waterbodies are not part of a geometric 

network, so automating the selection process was limited 

to location or feature attributes, or both. Because the 1:1M 

waterbodies dataset should represent waterbodies in the 

National Atlas 1:2M waterbodies dataset and add detail, 

selection by locating where waterbodies coincided with 

National Atlas and VMAP0 waterbodies was attempted; 

NHD waterbodies that intersected waterbodies represented 

in National Atlas and VMAP0 were selected. In several 

cases, spatial shifts or offsets in the VMAP0 waterbodies 

dataset were substantial enough that the intersection was 

not efficient at selecting the NHD waterbody polygons 

that correlated with VMAP0 waterbodies. The spatial shifts 

in the VMAP0 dataset made selection by location inconsistent, so location could not be the sole selection criterion.

Established Production Method

The production method that was established for selecting waterbodies for inclusion in the 1:1M dataset combined 

a waterbody area threshold with manual verification and 

addition of features represented in the National Atlas 1:2M 

waterbodies dataset. An area threshold was used to automate 

waterbody selection. Different thresholds were tried until a 

minimum area was determined that resulted in selection of 

most waterbodies represented in the National Atlas 1:2M 

waterbodies dataset. Waterbodies with an area greater than 

1 square kilometer (0.3861 square mile) were selected and 

included in the 1:1M selection, then waterbodies with an area 

greater than 0.5625 square kilometer (0.2172 square mile) 

that coincided with National Atlas 1:2M waterbodies were 

manually added to the selection.

Simplification

Geometric simplification of features commonly is 

done to create less complex lines for maps or to reduce 

data storage requirements (Neuffer and others, 2004). The 

features in the 1:1M streams and waterbodies datasets were 

simplified to create less complex features as well as to reduce 

storage requirements. One use of the 1:1M streams and 

waterbodies datasets is for cartographic representation, which 

requires that the features display an appropriate level of detail 

at 1:1M. Additionally, the 1:1M streams and waterbodies 

datasets are intended to facilitate hydrologic analysis, so the 

simplification process cannot disable networking capabilities. Simplification of features reduces the size of the dataset, 

which makes data transfer and analysis more efficient. Feature 

geometry thus was simplified for increased usability and 

processing speed. Another option would have been to keep the 

geometry as detailed as possible and allow the user to simplify 

as necessary. 

Reaches indicated in the feature selection process were 

exported as a new feature class and then simplified using 

the Bend Simplify algorithm of the ESRI Simplify Line tool 

(ESRI, 2008b) with a tolerance of 500 meters. The Bend 

Simplify algorithm modifies the line geometry between 

end nodes by analyzing and modifying non-critical bends 

relative to a semicircle with a radius of 500 meters. The 

result is a simplified line that maintains the general shape 

of the original segment without moving the end nodes. The 

segment end nodes were preserved to maintain the importance of the reach codes. Combining and merging contiguous segments would greatly reduce file size by allowing 

more geometric simplification, but the reach codes are an 

important aspect of the stream network that allow for hydrologic analysis. The new, simplified and generalized subregional streams dataset was appended into a regional streams 

feature class and then tested for network connectivity. A 

new regional geometric network was created, and upstream 

traces were used to search for missing or disconnected 

reaches.

Similarly, waterbodies were simplified using the Bend 

Simplify algorithm of the ESRI Simplify Line tool (ESRI, 

2008b) with a tolerance of 500 meters (fig. 5). The simplification process occasionally caused topological errors where 

the modified waterbody boundaries overlapped adjacent 

waterbodies or where slivers (thin, erroneous features) were 

introduced between waterbodies that share a boundary. The 

new, simplified and generalized subregional waterbodies datasets were appended into a regional waterbodies feature class 

and tested for topological errors. Waterbodies that overlapped 

other waterbodies and slivers along shared waterbody boundaries were corrected.
0 5 10 MILES

Projection: Albers equal area

Central Meridian: -96

Standard Parallel 1: 29.5

Standard Parallel 2: 45.5

Latitude of Origin: 23

Linear Unit: Meter

Location map

EXPLANATION

Lake or reservoir

Swamp or marsh

(A) (B)

Yellowstone

Lake

Yellowstone

Lake

Area enlarged

N N

Refinement 11

Refinement

Streams

After selecting streams from the NHD for the 1:1M 

dataset, areas of stream-density disparity were apparent in 

the stream network when viewing the dataset at a regional 

scale. These areas of disparity followed the boundaries of 

the IMW map sheets. Maps covering the United States in 

the IMW series (figs. 1, 2) were compiled during 1934–78 

by four different agencies. As a result, the density of the 

stream network can differ from map to map, which means 

that the streams at the boundaries of each map do not always 

exactly match those at the boundaries of adjoining maps. 

When the paper maps were scanned and mosaicked, artifacts 

(sometimes called map faults) from the artificial boundaries 

between each map in the series were evident. These map faults 

occurred in areas where the density of cartographically 

represented physical features on one map was distinctly 

different from the density of such features on adjoining 

maps. 

Because streams were selected for the 1:1M dataset partly 

on the basis of whether they were on an IMW map sheet, 

artifacts of the stream-density disparity carried over to the 

1:1M hydrography dataset (fig. 6). Because the 1:1M dataset 

is intended to fill the needs for cartographic products and 

hydrologic analysis, density artifacts needed to be removed 

and stream density needed to be equalized across IMW 

boundaries. The density disparity was analyzed using the ratio 

of the 1:1M stream density to the National Atlas 1:2M stream 

density within polygons that resulted from the intersection of 

the NHD subregion boundaries and the IMW sheet boundaries. After the densest areas were identified and quantified with 

this ratio, streams were prioritized and selected streams were 

removed in these dense areas to create a uniform appearance 

across the stream network at a regional scale. 

Figure 5. (A) Original National Hydrography Dataset 1:100,000-scale waterbody polygon with 2,297 vertices and (B) simplified 

1:1,000,000-scale waterbody polygon with 1,032 vertices.
12 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

Figure 6. Preliminary 1:1,000,000-scale streams dataset showing stream-density disparity along adjoining boundaries of International Map of the World map sheets, continental United States. 
Refinement 13

Stream-Density Analysis

The stream-density disparities were visibly apparent 

(fig. 7A), but to follow an objective, repeatable process, the 

disparities needed to be quantitatively described and identified. The NHD subregion boundaries were intersected with the 

IMW map sheet boundaries to create polygons for analysis of 

the density disparities in the unrefined 1:1M dataset. Density 

of streams was calculated for the 1:1M unrefined dataset and 

the National Atlas 1:2M dataset in each of the density analysis 

polygons. Stream density is defined as the total linear length, 

in kilometers, of all streams in a density polygon divided by 

the density polygon area, in square kilometers. 

The National Atlas 1:2M and the NHD 1:100K streams 

datasets represent water features in different ways. For 

example, large streams have a right and left bank in the 

National Atlas streams dataset, and they are represented as 

a single flowline in the NHD that might or might not have a 

corresponding NHD waterbody. To facilitate comparison of 

1:1M stream density to National Atlas 1:2M stream density, 

the National Atlas 1:2M streams lengths were adjusted and 

normalized using feature types to apply weighting factors to 

be comparable to the NHD feature types (table 2). After the 

density of streams was calculated, the ratio of 1:1M stream 

density to 1:2M stream density was analyzed. Regions requiring density reduction were identified on the pre-refinement 

map (fig. 8A) as areas with high-density ratios adjacent to 

areas with low-density ratios that share a rectilinear boundary. 

High-ratio regions on the pre-refinement map indicate that the 

preliminary 1:1M streams dataset might be too dense compared to the National Atlas 1:2M streams dataset. 

Stream-Density Adjustment

After the densest regions were identified, streams were 

removed from the 1:1M dataset in those regions to create a 

more uniform level of stream density. Streams were selected 

to be removed on the basis of indicated flow (perennial or 

intermittent), name attributes, and length to confluence. The 

headwater reach of a stream to be removed was selected, and 

then a tool traced the network downstream from the selected 

reach to the first confluence, removing the connected segments 

along the way. After selected reaches were removed, another 

tool was used to clean up any small headwater reaches that 

might have been missed in the removal process. Removing the 

selected streams resulted in stream density of the 1:1M dataset 

more closely matching that of the National Atlas 1:2M streams 

(figs. 7B, 8B).

Figure 7. Example of stream-density disparity along International Map of the World (IMW) map sheet boundary (A) before and (B) after 

refinement of the 1:1,000,000-scale streams dataset.

89° 88° 87°

32°

0 30 60 MILES

(A)

2,592

3,356

2,568

2,189

89° 88° 87°

32°

(B)

IMW map sheet boundary

IMW map sheet boundary

EXPLANATION

2,189 Number of stream

segments
14 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

Figure 8. Density discrepancy polygons (based on intersection of International Map of the World map sheet boundaries and National 

Hydrography Dataset subregion boundaries) symbolized by the ratio of density in the 1:1,000,000-scale (1:1M) stream network to density 

in the National Atlas 1:2,000,000-scale (1:2M) stream network (A) before and (B) after refinement of the 1:1M streams dataset.
Refinement 15

The last step in the density-adjustment process for 

streams was to plot all 1:1M streams for review by cartographers. The cartographers examined the density of the streams 

and determined whether streams should be added to or deleted 

from the 1:1M dataset. Using their knowledge of United States 

streams and referencing State base maps and other sources, 

the cartographers added a final level of refinement to the 1:1M 

streams dataset (fig. 9).

Evaluation of Stream-Density Adjustment 

After the initial analysis of stream density and the subsequent adjustment of density along the map faults, the resulting 

density ratios were statistically analyzed to evaluate the results 

for consistency across the dataset. Because some of the density 

polygons were relatively small compared to the majority of the 

density polygons, a small number of outlying density ratios 

were present. Consequently, the upper 2 percentiles of the 

adjusted and unadjusted density ratios were removed from the 

analysis described here. 

Summary statistics of the density ratios before and after 

adjustment are tabulated in table 3. All density ratios and 

computed statistics are reported to three significant figures. 

Quantitatively, 90 percent of the unadjusted density ratios are 

within the range of 0.750–2.94 about the median value of 1.77; 

90 percent of the adjusted density ratios are within the range 

of 0.822–2.45 about the median value of 1.62. A common 

expectation would be that a 1:1M map would have about twice 

the “detail” of a 1:2M map. The unadjusted density ratio mean 

is 1.82 and the adjusted density mean is 1.64—both approaching a mean of 2. The density differences likely are due to the 

subjective interpretation of the 1:2M and 1:1M map compilers 

and the nature of the features in the base data. 

To illustrate the adjusted and unadjusted density-ratio 

distributions, superimposed histograms were created (fig. 10). 

The overall range of the density ratios (0 to 4.73) was equally 

divided into 50 partitions (bins), and frequency counts were 

computed for each bin. Area-weighting (rescaling in proportion to density polygon area) was done on the computed 

frequency counts. In this manner, each density ratio is represented in proportion to its contributing area to the dataset. 

Using the means and standard deviations of the unadjusted and 

adjusted density ratios, theoretical normal distributions (probability density functions) were fit to the histograms (Helsel 

and Hirsch, 2000). Because the theoretical distributions are in 

probability space, the frequency counts of the histograms were 

Table 2. Weighting factors used to adjust National Atlas 1:2,000,000-scale streams features to allow for comparison to 1:1,000,000-

scale streams.

[NHD, National Hydrography Dataset]

Feature type Weighting factor Rationale

Apparent limit Omit Not present in NHD flowline

Aqueduct Omit Not present in NHD flowline

Canal 1 Equivalent features in NHD flowline

Canal intermittent 1 Equivalent features in NHD flowline

Closure line Omit Not present in NHD flowline

Dam Omit Not present in NHD flowline

Falls Omit Not present in NHD flowline

Intracoastal waterway 1 Check if in NHD

Left bank .5 Assumes parallel stream banks, on average

Right bank .5 Assumes parallel stream banks, on average

Shoreline .3 Assumes approximate circular waterbody, on average

Shoreline intermittent .3 Assumes approximate circular waterbody, on average

Stream 1 Equivalent features in NHD flowline

Stream intermittent 1 Equivalent features in NHD flowline

Braided stream 1 Equivalent features in NHD flowline

Null Omit Not present in NHD flowline
16 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

Figure 9. Density-adjusted 1:1,000,000-scale streams dataset showing less density disparity (compared to that shown in fig. 6) along adjoining boundaries of International Map of the World map sheets, continental United States. 
Refinement 17

rescaled such that the integrals (areas) of each histogram over 

their domains equaled unity. Thus, both histograms and theoretical distributions share a common vertical scale for comparison purposes. The means of the unadjusted and adjusted 

density-ratio distributions also are shown in figure 10 as an 

indication of central tendency.

As the histograms in figure 10 show, the refinement 

procedure resulted in a slight shift of the distribution toward 

lower density ratios. This was expected because the procedure consisted of stream removal to enforce continuity among 

adjacent density polygons. However, the narrower distribution 

of the adjusted density ratios (as also indicated by smaller 

interquartile range and standard deviation [table 3]) implies 

that the adjustment procedure resulted in stream densities 

more uniformly distributed with respect to the reference 1:2M 

dataset.

Waterbodies

The methods used for waterbody feature selection 

and simplification preserve attributes and general geometry 

of the selected features. To refine the dataset to National 

Figure 10. Area-weighted histograms and fitted normal distributions of unadjusted and adjusted stream-density ratios.

Table 3. Summary statistics of unadjusted and adjusted streamdensity ratios.

[All values dimensionless]

Statistic Unadjusted Adjusted

Number of values 528 528

Minimum 0 0

First quartile 1.43 1.36

Median 1.77 1.62

Mean 1.82 1.64

Third quartile 2.15 1.91

Maximum 4.73 4.56

Interquartile range .717 .550

Standard deviation .680 .556

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

DENSITY RATIO, DIMENSIONLESS

AREA−WEIGHTED PROBABILITY DENSITY, DIMENSIONLESS

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

EXPLANATION

Unadjusted density ratio

Adjusted density ratio

Fitted normal distribution to unadjusted density ratio

Fitted normal distribution to adjusted density ratio

Mean of unadjusted density ratio

Mean of adjusted density ratio
18 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

Atlas cartographic and attribute standards, feature geometry 

and name attributes were adjusted. NHD waterbody polygons split by quadrangle (topographic map) boundaries were 

merged and extended to represent the actual waterbody boundary. Name attributes that differed from National Atlas 1:2M 

names were verified and reconciled.

Feature Geometry Modifications

Some of the source NHD waterbody polygons were 

split along 1:100K and 1:24K topographic map boundaries 

or 1:63,360-scale topographic map boundaries for Alaska. 

These split polygons could have been created when the 

polygons were digitized from topographic maps. For example, if one topographic map showed a waterbody, but the 

adjacent topographic map did not show a waterbody or indicated a different name for that waterbody, the waterbody 

commonly was split by the map boundary. Because waterbodies often were divided into multiple parts, the feature 

selection process missed parts with an area less than the 

inclusion threshold, which caused waterbodies to have an 

unnatural edge created by the topographic map boundary 

(fig. 11). By following the topographic map boundaries 

laterally and vertically, the split or misaligned polygons, 

or both, were identified. The polygons were merged or 

reshaped, or both, to correlate with waterbodies shown on 

USGS 1:250K, 1:100K, and 1:24K digital topographic maps 

available as a Web Map Service (U.S. Geological Survey, 

2005b).

Name Updates

Many NHD GNIS names did not match or were missing from features that were named in the National Atlas 

1:2M waterbodies dataset. Polygons that intersected named 

National Atlas 1:2M waterbodies were examined for name 

consistency. The name was verified to match the name listed 

in the National Atlas 1:2M waterbodies dataset. If there was 

a discrepancy, the USGS 1:250K, 1:100K, and 1:24K topographic maps were used to verify the correct name, and the 

attribute was updated. Overall, 304 names were modified from 

the original GNIS name.

Figure 11. Example of (A) unmodified waterbodies and (B) corresponding modified waterbodies.
Selected References 19

Summary

The development of a 1:1,000,000-scale (1:1M) nationwide hydrography dataset is critical to meeting the evolving needs of the National Atlas of the United States. During 

2006–09, the U.S. Geological Survey (USGS), in cooperation 

with the National Atlas of the United States, produced a 1:1M 

hydrography dataset comprising streams and waterbodies for 

the entire United States, including Puerto Rico and the U.S. 

Virgin Islands, for inclusion in the recompiled National Atlas. 

The focus of this production effort was to create datasets 

of 1:1M streams and waterbodies, with appropriate stream 

density, using a method for selecting features from the USGS 

National Hydrography Dataset (NHD) that would be consistent across the entire United States and that also would maintain network connectivity. Additionally, the vast cartographic 

knowledge embedded in the National Atlas and other datasets 

was to be retained. This report documents the methods used 

to select, simplify, and refine features in the 1:100,000-scale 

(1:100K) (1:63,360-scale in Alaska) NHD to create the 

national 1:1M hydrography dataset. 

Several readily available, small-scale, nationwide hydrographic datasets exist, although none of these ancillary datasets singularly fills the needs of the National Atlas recompilation effort. Primary ancillary datasets for this project included 

the existing National Atlas 1:2M streams and waterbodies, 

the Vector Map Level 0 (VMAP0), and the International Map 

of the World (IMW). The USGS Elevation Derivatives for 

National Applications (EDNA) dataset, digital orthoimagery, 

and digital topographic maps were used as secondary datasets. 

The first step in creating the new 1:1M dataset was to 

address feature selection and optimal data density in the 

streams network. Several existing methods were evaluated: 

for example the ArcGIS Utility Network Analyst extension, 

NHD name hierarchy, hydrologic derivatives, and NHDPlus

Thinner Codes. The production method that was established 

for selecting features for inclusion in the 1:1M dataset uses a 

combination of the existing attributes and network in the 

NHD and several of the concepts from the methods that were 

evaluated. 

Headwater reaches were selected manually on the basis 

of whether the stream was represented in the National Atlas, 

VMAP0, and IMW hydrography datasets, which served as 

primary indicators of 1:1M stream density. The downstream 

trace algorithm used in this project was written in Visual Basic 

for Applications using ArcObjects and implemented as an 

easy-to-use tool within the ArcMap environment. The tool 

traces downstream from the selected headwater reaches and 

attributes reaches for inclusion in the 1:1M dataset on the basis 

of a set of criteria. If the tool encounters a reach that does not 

meet any of the selection criteria, the algorithm stops processing to allow the analyst to select the appropriate downstream 

reach on the basis of digital orthoimagery, georeferenced 

topographic maps, or the EDNA dataset. After all reaches 

were selected, the proposed 1:1M network was examined for 

connectivity. 

The process for creating the 1:1M waterbodies dataset 

required a similar approach to that used for the 1:1M streams 

dataset. The NHD waterbodies are not part of a geometric 

network, so automating the selection process was limited to 

location or feature attributes, or both. The production method 

that was established for selecting waterbodies for inclusion in 

the 1:1M dataset combined a waterbody area threshold with 

manual verification and addition of features represented in the 

National Atlas 1:2M waterbodies dataset.

Geometric simplification of features, commonly done to 

create less complex lines for maps or to reduce data storage 

requirements, was the next step. Stream reaches and waterbodies indicated in the feature selection process were exported in 

a geographic information system as new feature classes and 

then simplified using the Bend Simplify algorithm of the ESRI 

Simplify Line tool with a tolerance of 500 meters.

The final step was refinement of the 1:1M streams and 

waterbodies. After selecting streams from the NHD for the 

1:1M dataset, areas of stream-density disparity were apparent 

in the stream network when viewing the dataset at a regional 

scale. Because streams were selected for the 1:1M dataset 

partly on the basis of whether they were on an IMW map 

sheet, artifacts of stream-density disparity between adjacent 

sheets carried over to the 1:1M hydrography dataset. The 

stream-density disparities were visibly apparent, but to follow 

an objective, repeatable process, the disparities needed to 

be quantitatively described and identified. After the densest 

areas were identified, streams were removed from the 1:1M 

dataset to create a more uniform level of stream density. The 

last step in the density-adjustment process for streams was to 

plot all 1:1M streams for review by cartographers. Refinement 

of waterbodies involved fixing split waterbody polygons and 

name discrepancies using the 1:100K and 1:24K topographic 

map boundaries or 1:63,360-scale topographic map boundaries 

in Alaska for reference.

Selected References

American Geographical Society, 1934, NH 13 Chihuahua: International Map of the World map series, scale 

1:1,000,000.

American Geographical Society, 1937, NG 14 Monterrey: International Map of the World map series, scale 

1:1,000,000.

American Geographical Society, 1937, NH 12 Sonora: International Map of the World map series, scale 1:1,000,000.

Army Map Service, 1955, NI 13 Santa Fe: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1955, NI 18 Hatteras: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1955, NJ 14 Wichita: International Map of 

the World map series, scale 1:1,000,000.
20 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

Army Map Service, 1955, NJ 18 Chesapeake Bay: International Map of the World map series, scale 1:1,000,000.

Army Map Service, 1955, NK 12 Great Salt Lake: International Map of the World map series, scale 1:1,000,000.

Army Map Service, 1955, NK 13 Cheyenne: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1955, NK 19 Boston: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1955, NL 12 Yellowstone: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1955, NL 13 Big Horn Mountains: International Map of the World map series, scale 1:1,000,000.

Army Map Service, 1955, NL 14 Dakotas: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1955, NL 15 Minneapolis: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NH 15 White Lake: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NH 17 Jacksonville: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NI 15 Vicksburg: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NO 3, 4 Bristol Bay: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NO 5, 6 Kodiak: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NO 7, 8 Sitka: International Map of 

the World map series, scale 1:1,000,000.

Army Map Service, 1956, NP 3, 4 Bethel: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NP 5, 6 Anchorage: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NP 7, 8 Whitehorse: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NQ 3, 4 Nome: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NQ 5, 6 Fairbanks: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NR 3, 4 Barrow: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NR 5, 6 Umiat: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1956, NR 7, 8 Mackenzie Bay: International Map of the World map series, scale 1:1,000,000.

Army Map Service, 1959, NG 17 Florida Keys: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1959, NH 16 Mobile: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1959, NI 10 Point Conception: International Map of the World map series, scale 1:1,000,000.

Army Map Service, 1959, NI 12 Gila River: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1959, NI 14 Dallas: International Map of 

the World map series, scale 1:1,000,000.

Army Map Service, 1959, NJ 10 San Francisco Bay: International Map of the World map series, scale 1:1,000,000.

Army Map Service, 1959, NJ 12 Grand Canyon: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1959, NJ 16 Louisville: International Map 

of the World map series, scale 1:1,000,000.

Army Map Service, 1959, NK 10 Mount Shasta: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1959, NK 11 Owyhee River: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1959, NK 14 Platte River: International 

Map of the World map series, scale 1:1,000,000.

Army Map Service, 1960, NL 11 Snake River: International 

Map of the World map series, scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1967, 

NM 11 Kootenay Lake: International Map of the World map 

series, scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1967, 

NM 13 Regina: International Map of the World map series, 

scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1967, 

NM 14 Winnipeg: International Map of the World map 

series, scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1967, 

NM 15 Lake Of The Woods: International Map of the World 

map series, scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1967, 

NM 9, 10 Vancouver: International Map of the World map 

series, scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1968, 

NN 8, 9 Prince Rupert: International Map of the World map 

series, scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1969, 

NL 17 Sudbury: International Map of the World map series, 

scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1969, 

NM 16 Lake Nipigon: International Map of the World map 

series, scale 1:1,000,000.
Selected References 21

Canada Department of Energy, Mines, and Resources, 1969, 

NO 9 Dease Lake: International Map of the World map 

series, scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1970, 

NM 12 Lethbridge: International Map of the World map 

series, scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1974, 

NL 18 Ottawa: International Map of the World map series, 

scale 1:1,000,000.

Canada Department of Energy, Mines, and Resources, 1975, 

NQ 7, 8, 9 Peel River: International Map of the World map 

series, scale 1:1,000,000. 

ESRI, 2006, Using ArcObjects as tool input: accessed May 1, 

2009, at http://webhelp.esri.com/arcgisdesktop/9.2/index.

cfm?id=739&pid=727&topicname=Using_ArcObjects_as_

tool_input

ESRI, 2007, An overview of ArcMap: accessed May 1, 

2009, at http://webhelp.esri.com/arcgisdesktop/9.2/index.

cfm?id=176&pid=175&topicname=An_overview_of_

ArcMap

ESRI, 2008a, Tracing on geometric networks: accessed May 

1, 2009, at http://webhelp.esri.com/arcgisdesktop/9.2/

index.cfm?id=5573&pid=5564&topicname=Tracing_on_

geometric_networks

ESRI, 2008b, Simplify Line: accessed May 1, 2009, at http://

webhelp.esri.com/arcgisdesktop/9.2/index.cfm?id=1581&pi

d=1575&topicname=Simplify_Line_(Data_Management)

ESRI, 2008c, Georeferencing a raster dataset: accessed April 

30, 2009, at http://webhelp.esri.com/arcgisdesktop/9.2/

index.cfm?TopicName=Georeferencing_a_raster_dataset

Estes, J.E., Kline, K.D., Hemphill, J.J., Scepan, J., and 

Holland, P., 2001, The imperative for proactive cooperative 

national mapping strategies in the new millennium: Institute of Electrical and Electronics Engineers 2001 International Geoscience and Remote Sensing Symposium, v. 3, 

p. 1,478–1,480.

Heffernan, M., 2002, The politics of the map in the early 

twentieth century: Cartography and Geographic Information 

Science, v. 29, no. 3, p. 207–226.

Helsel, D.R., and Hirsch, R.M., 2000, Statistical methods in 

water resources (4th ed.): Amsterdam, The Netherlands, 

Elsevier Science B.V. Studies in Environmental Science, 

v. 49, 529 p.

International Steering Committee for Global Mapping, 2007, 

Global map specifications version 1.3: accessed July 1, 

2008, at http://www.iscgm.org/cgi-bin/fswiki/wiki.cgi?actio

n=ATTACH&page=Documentation&file=Global+Mapping

+Version+1%2E3+Specifications%2Epdf 

International Steering Committee for Global Mapping, 2008, 

Global Mapping home page: available at http://www.iscgm.

org/.

National Atlas of the United States, 2006, Streams and waterbodies: accessed October 1, 2008, at http://nationalatlas.

gov/atlasftp.html?openChapters=chpwater#chpwater.

National Atlas of the United States, 2008, Where we are: 

available at http://nationalatlas.gov/.

National Geospatial-Intelligence Agency, 1998, Vector map 

level 0 (VMAP0): Scale 1:1,000,000.

Neuffer, D., Bell, M., and Woodsford, P., 2004, Cartographic 

generalisation on the basis of model generalisation: Symposium Praktische Kartographie Königslutter 2004.

Pearson, A., Taylor, D.R.F., Kline, K.D., and Heffernan, M., 

2006, Cartographic ideals and geopolitical realities—International maps of the world from the 1890s to the present: 

The Canadian Geographer, v. 50, no. 2, p. 149–176.

Stanislawski, L., Starbuck, M., Finn, M., and Usery, E.L., 

2005, Generalization for The National Map with emphasis on the National Hydrography Dataset, in Twenty-Fifth 

Annual ESRI User Conference, San Diego, California, July 

25–29, 2005, Proceedings: ESRI.

U.S. Environmental Protection Agency, 1994, History of the 

U.S. EPA’s river reach file—A national hydrographic database available for ARC/INFO applications: accessed May 1, 

2009, at http://www.epa.gov/waters/doc/historyrf.pdf

U.S. Environmental Protection Agency and U.S. Geological 

Survey, 2008, NHDPlus user guide: accessed July 10, 2008, 

at ftp://ftp.horizon-systems.com/NHDPlus/documentation/

NHDPLUS_UserGuide.pdf

U.S. Geological Survey, 1945, NH 14 Austin: International 

Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1945, NL 10 Cascade Range: International Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1947, NI 11 Los Angeles: International Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1966, NJ 11 Mount Whitney: International Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1966, NJ 13 Pikes Peak: International 

Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1966, NL 16 Lake Superior: International Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1968, NI 16 Lookout Mountain: International Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1968, NL 19 Quebec: International 

Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1970, NK 15 Des Moines: International Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1970, The national atlas of the United 

States of America: Washington, D.C., 417 p.
22 Production of a National 1:1,000,000-Scale Hydrography Dataset for the United States

U.S. Geological Survey, 1971, NJ 15 Ozark Plateau: International Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1971, NN 3, 4 Cold Bay: International Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1972, NJ 17 Blue Ridge: International 

Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1973, NK 16 Chicago: International 

Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1974, NK 17 Lake Erie: International 

Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1974, NK 18 Hudson River: International Map of the World map series, scale 1:1,000,000.

U.S. Geological Survey, 1978, NI 17 Savannah: International 

Map of the World map series, scale 1:1,000,000. 

U.S. Geological Survey, 2002, Map scales: U.S. Geological 

Survey Fact Sheet 015–02, 2 p.

U.S. Geological Survey, 2005a, Elevation derivatives for 

national applications (EDNA): available at http://edna.usgs.

gov/.

U.S. Geological Survey, 2005b, GISDATA map studio: available at http://gisdata.usgs.gov/.

U.S. Geological Survey, 2006a, National elevation dataset: 

available at http://ned.usgs.gov/.

U.S. Geological Survey, 2006b, National Hydrography Dataset 

(1:100,000-scale): accessed October 1, 2006, at ftp://nhdftp.

usgs.gov/SubRegions/Medium/.

U.S. Geological Survey, 2006c, National Hydrography Dataset 

(1:63,360-scale): accessed October 1, 2006, at ftp://nhdftp.

usgs.gov/SubRegions/High/.

U.S. Geological Survey, 2007, Geographic Names Information 

System–GNIS: available at http://nhd.usgs.gov/gnis.html

U.S. Geological Survey, 2008, National Hydrography Dataset: 

available at http://nhd.usgs.gov/.

Publishing support provided by

Lafayette Publishing Service Center

Information regarding water resources in Texas is available at 

http://tx.usgs.gov/

Glossary

Feature class A collection of geometric representations of 

real-world features and their associated attributes.

Node Vertex at the end or beginning of a line segment.

Topology Refers to the spatial relation among features in a 

feature class, for example whether features overlap each other 

or have gaps between them.

Vertex (vertices [plural]) Coordinate pairs that define the 

shape of a line or polygon feature.