Development of a Land Use Database for the Little 

Blackwater Watershed, Dorchester County, Maryland 

By Lesley E. Milheim, John W. Jones, and Roger A. Barlow 

Open-File Report 2007–1309 

U.S. Department of the Interior 

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

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2007 

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Suggested citation: 

Milheim, L.E., Jones, J.W., and Barlow, R.A., 2007, Development of a land use database for the Little 

Blackwater River watershed, Dorchester County, Maryland: U.S. Geological Survey Open-File Report 2007-

1309, 12 p., available online at http://pubs.usgs.gov/of/2007/1309/. 

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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 material contained within this report. 

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Contents 

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

Classification Scheme .......................................................................................................................................................2

Input Data.............................................................................................................................................................................2

National Agricultural Imagery Program Dataset for Dorchester County, Maryland..........................................2

Digital Elevation Model..................................................................................................................................................2

Study Area .......................................................................................................................................................................3

Roads ................................................................................................................................................................................3

Streams.............................................................................................................................................................................3

Digital Orthophoto...........................................................................................................................................................3

Software...............................................................................................................................................................................3 

Processing Steps................................................................................................................................................................3

Data Collection................................................................................................................................................................3

Quality Assurance/Quality Control ..............................................................................................................................4

Metadata..........................................................................................................................................................................4

Results ..................................................................................................................................................................................4

References Cited ................................................................................................................................................................8

Figures 

Figure 1. Lidar-based digital elevation model (DEM) of the Little Blackwater River watershed study area 

(44.5 square kilometers). Study area delineated by a red line (main map and index map). Watershed 

boundary includes a 100-meter buffer. Egypt Road project delineated by an orange line. Stream gage 

location identified by a blue dot.......................................................................................................................................5 

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Figure 2. Land use polygon boundaries (black lines) within the Little Blackwater River watershed study 

area overlain on National Agricultural Imagery Program (NAIP) orthoimagery of June-July 2005. Study area 

delineated by red line. .......................................................................................................................................................6

Figure 3. Classified land use polygons within the Little Blackwater River watershed study area overlain on 

National Agricultural Imagery Program (NAIP) orthoimagery of June-July 2005..................................................7

Tables 

Table 1. Summary of land use within the Little Blackwater River watershed, June-July 2005. ..........................4
Development of a Land Use Database for the Little 

Blackwater River Watershed, Dorchester County, 

Maryland 

By Lesley E. Milheim, John W. Jones, and Roger A. Barlow 

Introduction 

Many agricultural and forested areas in proximity to National Wildlife Refuges (NWR) are 

under increasing economic pressure to develop lands for commercial or residential development. The 

upper portion of the Little Blackwater River watershed – a 27 square mile area within largely low-lying 

Dorchester County, Maryland, on the eastern shore of the Chesapeake Bay – is important to the U.S. 

Fish and Wildlife Service (USFWS) because it flows toward the Blackwater National Wildlife Refuge 

(BNWR), and developmental impacts of areas upstream from the BNWR are unknown. 

One of the primary concerns for the refuge is how storm-water runoff may affect living 

resources downstream. The Egypt Road project (fig. 1), for which approximately 600 residential units 

have been approved, has the potential to markedly change the land use and land cover on the west bank 

of the Little Blackwater River. In an effort to limit anticipated impacts, the Maryland Department of 

Natural Resources (Maryland DNR) recently decided to purchase some of the lands previously slated 

for development. Local topography, a high water table (typically 1 foot or less below the land surface), 

and hydric soils present a challenge for the best management of storm-water flow from developed 

surfaces. 

A spatial data coordination group was formed by the Dorchester County Soil and Conservation 

District to collect data to aid decisionmakers in watershed management and on the possible impacts of 

development on this watershed. Determination of streamflow combined with land cover and 

impervious-surface baselines will allow linking of hydrologic and geologic factors that influence the 

land surface. This baseline information will help planners, refuge managers, and developers discuss 

issues and formulate best management practices to mitigate development impacts on the refuge. 

In consultation with the Eastern Region Geospatial Information Office, the dataset selected to be 

that baseline land cover source was the June-July 2005 National Agricultural Imagery Program (NAIP) 

1-meter resolution orthoimagery of Maryland. This publicly available, statewide dataset provided 

imagery corresponding to the closest in time to the installation of a U.S. Geological Survey (USGS) 

Water Resources Discipline gaging station on the Little Blackwater River. It also captures land cover 

status just before major residential development occurs. This document describes the process used to 

create a land use database for the Little Blackwater watershed. 

1
Classification Scheme 

The first step in any land use mapping effort is the design of a land use classification and 

mapping scheme that is appropriate for the intended use of the data. The USGS and Maryland DNR 

discussed classification requirements on August 10, 2006, at the Maryland Department of Natural 

Resources in Annapolis. After consultation the Dorchester County Soil and Conservation Service, the 

group decided to use a modified Anderson Level I (Anderson, 1972) tailored to the major classes of 

land use and land cover observed in the watershed. Use of an Anderson Level II classification was 

viewed as ineffective in terms of time and usefulness. Classes used for this study include: 

Commercial – includes churches, schools, and governmental, construction, and manufacturing, 

grounds (non-residential), buildings and parking lots, 

Transportation – primarily based on Maryland State Highway Administration road centerline 

shapefile as well as roads associated with new construction, railroad bed, and the airport grounds, 

Residential – residential neighborhoods and grounds including farmhouses if they were distinct 

from farm buildings, 

Agricultural – crop fields, chicken houses, barns, equipment, and other storage buildings and 

associated grounds, 

Open area – areas that are not associated with other uses and may be subject to developmental 

pressure, 

Forest – predominance of forested land. In this area, much of the forest is wet because of the low 

elevation and gradient. The forest class also includes relatively open areas where there was evidence of 

clearing and new forest growth. The area has a history of cyclic forest clearance, 

Water – open water in wetlands, forests, agricultural areas, and stormwater mitigation ponds. 

Ponds are scattered throughout the watershed where farmers have allowed water to pond so that other 

areas may be cultivable and are often smaller than the stated minimum area of 0.25 acre (criteria 

established at the August 10, 2006, meeting). However, the frequency of occurrence provides an 

indication of the general wetness within this watershed and, therefore, they were mapped, 

Wetland – wet forest along drainage areas that may include limited marsh. The distinction 

between this classification and forest is very subjective, 

Disturbed area – areas prepared for construction and actual construction sites. 

Input Data 

To map land use according to the classification scheme specified, the following input data were 

used. 

National Agricultural Imagery Program Dataset for Dorchester County, Maryland 

This June-July 2005 1-meter resolution agricultural (leaf-on) imagery (NAIP_Dorchester.sid) 

shown in figure 2 was used to visually identify land use and land cover within the Little Blackwater 

River watershed (http://dnrweb.dnr.state.md.us/gis/data/data.asp). 

Digital Elevation Model 

An ArcGRID containing the 2-meter resolution Lidar digital elevation model (DEM) 

(abovebnwr) for a subset of Dorchester County, Maryland (Figure 1.) was used to identify the watershed 

boundary. This dataset is the mosaic of the Lidar DEM subsets available from the Maryland Department 

of Natural Resources. The Lidar subsets used are: ab1331, ab1332, ab1333, ab1334, ab1335, ab1336, 

aa1331, aa1332, aa1333, aa1334,aa1335, aa1336, z1331, z1332, z1333, z1334, ab1341, ab1342, 

2
ab1343, ab1344, ab1345, ab1346, aa1341, aa1342, aa1343, aa1344, aa1345, aa1346, z1341, z1342, 

z1343, z1344, ab1351, ab1352, ab1353, ab1354, ab1355, ab1356, aa1351, aa1352, aa1353, aa1354, 

aa1355, aa1356, z1351, z1352, z1353, z1354, ab1361, ab1363, ab1365, aa1361, aa1363, aa1365, z1361, 

and z1363. 

Study Area 

These data (BufferedStudyArea.shp) identify the watershed boundary plus a 100-meter buffer 

(fig. 1.) for the Little Blackwater River. The file was generated from the digital elevation model above 

the USGS stream gage located approximately 1.5 miles downstream of the confluence of the Maple 

Dam Branch and the Little Blackwater River (lat. 38°30'06" N, long. 76°05'39" W) using the ArcMap 

9.0 Spatial Analyst Hydrology toolkit. It resembles earlier watershed boundaries for this area excluding 

the area east of the airport. 

Roads 

These data (SHA_cline_SA.shp) identify the center-lines for roads within the watershed. The 

original shapefile is available from the Maryland State Highway Administration website 

(http://www.marylandgis.net/SHAdata/list.asp) and was trimmed to the study area. 

Streams 

These data (SHA_streams_SA.shp) identify the streams within the watershed. The original 

shapefile is available from the Maryland State Highway Administration website 

(http://www.marylandgis.net/SHAdata/list.asp) and was trimmed to the study area. 

Digital Orthophoto 

These 4-meter resolution digital orthophotos (Cambr215.tif, Cambr315.tif, 1998) available from 

the Maryland Department of Natural Resources website 

(http://dnrweb.dnr.state.md.us/gis/data/data.asp), were used as ancillary data for interpretation. 

Software 

The following software packages were used to create the database. 

• Platform: Windows XP 

• Environmental Systems Research Institute (ESRI) ArcGIS Desktop 9.0 with Spatial Analyst 

Extension 

• Habitat Digitizer Extension Version 4 Created by Ken Buja (Ken.Buja@noaa.gov) of the National 

Oceanographic and Atmospheric Administration 

(http://ccma.nos.noaa.gov/products/biogeography/digitizer/index.html) 

Processing Steps 

Data Collection 

ArcMap 9.0 was used to collect the land use and land cover areas within study area from the 

agricultural imagery (NAIP_Dorchester.sid). Compilation was performed using the ArcMap editor and 

the Habitat Digitizer Extension. Each area was visually identified by linear patterns, texture, and color 

and digitized along the perceived visual boundary. Visual interpretation was performed within ArcMap 

at a scale of 1:1500 and at a screen resolution of 1280 x 1024 pixels. As each area was completed, it was 

classified with a unique numeric identifier (UNIQUE_ID) and a description. Additional comments were 

entered to clarify or question the assigned classification as needed. Areas under question were visited to 

3
ascertain the validity of the assigned class and update the record, as needed. Boundaries were clipped to 

the study area to create the final land use/land cover shapefile. The polygon areas were calculated and 

added to the attribute table. 

Quality Assurance/Quality Control 

Due to time and funding constraints, no formal statistical or sampling quality assurance/quality 

control measures were performed. Instead, the classified polygons were compared with the actual land 

use and land cover observed through an onsite visit in October 2006 to confirm the identified classes 

and evaluate questionable classifications. This comparison resulted in the updating of some polygon 

attributes to provide a greater consistency in the final set of classes. Recent development in the area 

precluded the confirmation of some sites interpreted as undeveloped land cover types, given the date of 

the source imagery. 

Metadata 

Metadata were generated using ArcCatalog and the Federal Geographic Data Committee 

(FGDC) ESRI template and are available as part of the shapefile contents. 

Results 

The process resulted in a shapefile (LBRW_LULC.shp) containing the land use/land cover for 

the Little Blackwater River watershed as depicted in the June-July 2005 agricultural imagery shown in 

figure 1. The land use polygons are shown unclassified in figure 2 over the agricultural imagery 

(NAIP_Dorchester.sid) and are shown as classified in figure 3. The summary of these results is shown 

in table 1. 

Table 1. Summary of land use within the Little Blackwater River watershed, June-July 2005. 

[Abbreviations: m2

, square meters; km2, square kilometers] 

UNIQUE_ID CLASSIFICATION COUNT OF 

POLYGONS AREA (km2

) PERCENT OF STUDY 

AREA 

1 Commercial 49 1.3 3.0 

2 Transportation 25 1.1 2.4 

3 Residential 127 1.6 3.5 

4 Agricultural 305 18.9 42.6 

5 Open area 107 2.5 5.7 

6 Forest 97 16.0 35.9 

7 Water 52 0.3 0.6 

8 Wetland 75 2.5 5.6 

9 Disturbed area 13 0.3 0.7 

Total 44.5 100.0

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Figure 1. Lidar-based digital elevation model (DEM) of the Little Blackwater River watershed study 

area (44.5 square kilometers). Study area delineated by a red line (main map and index map). Watershed 

boundary includes a 100-meter buffer. Egypt Road project delineated by an orange line. Stream gage 

location identified by a blue dot. 

5
Figure 2. Land use polygon boundaries (black lines) within the Little Blackwater River watershed study 

area overlain on National Agricultural Imagery Program (NAIP) orthoimagery of June-July 2005. Study 

area delineated by red line. 

6
Figure 3. Classified land use polygons within the Little Blackwater River watershed study area overlain 

on National Agricultural Imagery Program (NAIP) orthoimagery of June-July 2005. 

7
8

References Cited 

Anderson, J.R., Hardy, E.E., and Roach, J.T., 1972, A land-use classification system for use with 

remote-sensor data: U.S. Geological Survey Circular 671, 16 p.