ANDSCAPE L INES

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Geographic Information Systems INTRODUCTION

Geographic Information Systems (GIS) are used to input, store,

manipulate, analyze, and map spatial data. Although GIS is often

considered a type of computer system, the first GIS systems involved manual techniques to perform some of the same functions

now performed by computers. In the late 1960s, the noted landscape architect Ian McHarg popularized the technique of using

transparent film map overlays to perform landscape analysis, about

the time when computers were being configured with software for

rudimentary mapping. Computers and GIS software have become

much more sophisticated and can generate new data and maps far

faster than is possible by hand. The utility of GIS in cultural landscape

management is now universally recognized.

Perhaps because of its roots in landscape analysis, the analytical

capabilities of GIS are considered among the most important uses of

the technology. Given the necessary historic data, GIS can be a

powerful tool for examining cultural landscape changes over time.

For example, if a park has digitized historic land use maps that are

appropriately georeferenced, GIS can overlay the historic data on

current land use data to determine the magnitude and spatial extent

of the changes. GIS can also model or predict various outcomes of

different treatment alternatives presented in a Cultural Landscape

Report (CLR).

Mapping, or cartographic output, is another important use of GIS, and is

often valuable for more intuitive, less explicit, visual analysis. (See Figure

1.) For many years the quality of cartographic output available through

GIS software could not equal that achieved with manual methods or

computer aided drafting (CAD) systems. But this is no longer the case.

Numerous mapping tools are now available in most GIS packages,
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including desktop systems, which offer the added

benefit of being easy enough to learn and use for

even non-GIS specialists.

GIS also offers an efficient method for storing and

retrieving cultural landscape data. Unlike

hardcopy maps, digital data does not decay over

time (although the storage media may need to be

updated), is easily copied with no loss of data

quality, and requires little physical space. And

while CAD systems may be just as effective in

storing and retrieving spatial data, GIS is far

superior for managing attribute information; that

is, data describing spatial features, such as the

year in which a building was constructed.

APPLYING GIS TO CULTURAL

LANDSCAPE MANAGEMENT

The National Park Service (NPS) has used GIS

extensively to document and analyze cultural

landscapes. The system can provide cartographic

models analyzing the effect of visitor use and assist

planners in developing alternatives for a visitor

facility or placing roads and trails. GIS can also be

used for viewshed analysis in which the computer,

using a digital elevation model, generates a data

layer of all areas visible from critical points within a

park. This data layer can then be used in conjunction with data about neighboring properties to

predict how local planning, zoning, and development proposals might impact park views.

Figure 1. GIS map of an archeological survey. Jamestown National Historic Site. (Map courtesy of North Carolina State

University, n.d.)
G E O G R A P H I C I N F O R M A T I O N S Y S T E M S 3

For example, Manassas National Battlefield Park

used GIS to protect its viewshed. The park was

able to simulate the effects of a proposed shopping mall and office development within view of

the battlefield. This helped the NPS garner public

support to oppose the development and eventually stop the project.

Inventories of park cultural features have often

been facilitated by the use of GIS. (See Figure

2.) Using Global Positioning System (GPS)

receivers, Richmond National Battlefield collected locations of all earthworks inside the park.

The digital data was then entered directly into

the park’s database. The park also used GIS to

inventory and monitor every tree in its historic

orchard. Similar databases have been developed

at many parks throughout the national park

system.

TECHNICAL CONSIDERATIONS

Data

Data is a critical element in GIS and it represents

the biggest investment of resources. None of the

previously mentioned implementations of GIS in

cultural landscape management would have been

possible without good data. Poor or inadequate

data can lead to erroneous results, which is often

Figure 2. GIS plan of unauthorized digging in Spangler’s Woods. The plan indicates topography, circulation, and vegetation, along with

the location of digging. The plan was created using Atlas GIS and AutoCAD. Gettysburg National Military Park. (Plan courtesy of North

Carolina State University, n.d.)
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worse than having no data at all. Care must

always be taken to use data that is appropriate for

the task at hand.

Types of Data

There are two basic types of data used in GIS: vector

and raster. Vector data includes points, lines, or

polygons and has one set of attributes associated with

each feature. Raster data is a continuous area broken

into a regular grid of cells, each cell having a value

(attribute) associated with it. For example, a soil grid

might have the soil type found at each cell location.

The main difference between vector and raster data is

that vectors are feature-oriented and rasters are

landscape-oriented. Discrete data, such as a structure,

is better suited to a vector format, while continuous

data, such as slope, is better suited to a raster format.

Spatial data is usually separated into layers. A layer

represents a group of features with a common set

of attributes. For instance, roads, trails, soils, and

terrain aspect are all possible data layers. In some

cases, seemingly different features can be combined

into one layer if the attributes are general enough.

For example, roads and trails can be combined into

a single layer called transportation, with an attribute

describing whether the feature is a road or a trail.

Obtaining Data

Although obtaining data has always been, and

remains the single largest roadblock to developing

successful GIS applications, the tools available for

collecting data are more numerous and easier to

use than ever before. Some of the more popular

methods for cultural landscape data collection

include the following:

• Global Positioning Systems (GPS). This involves the use of hand-held receivers that

receive signals from satellites to determine the

user’s location on the ground. (See Landscape

Lines11: Global Positioning Systems.)

• Map scanning. Scanners have become a quick

and efficient method for entering data from old

maps and are much faster than hand-digitizing

on a digitizing table, although sometimes the

latter method must still be used. (See Figures 3

and 4.) A scanned image is converted from a

raster format to a line format through vectoring

software.

• Digital orthophotography. This is aerial imagery

in which all the distortion due to terrain,

camera angle, etc., is removed so that it is

essentially a photo map. Many software

packages allow “heads up” digitizing on a

computer monitor with the digital orthophoto

image displayed as a backdrop.

In the next few years the development of very

detailed satellite imagery may become a useful

source of data for cultural landscape management.

Storing Data

All georeferenced data must be stored in a

coordinate system and datum. Furthermore, to

use two or more data sets together, they must

be stored in the same coordinate system and

datum. There are many coordinate systems

available, including latitude/longitude and state

plane, but the one most commonly employed

within the NPS is the Universal Transverse

Mercator (UTM) system. This coordinate

system is based on a series of Transverse
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Mercator projections, each one having its own

set of parameters that control how the spatial

coordinates are displayed. There are 60 zones

encircling the earth corresponding to these

projections, each zone being six degrees of

longitude in width. Since each zone has its own

Transverse Mercator projection and set of

associated parameters, all data to be used

together must be stored in the same UTM zone.

There are two datums in widespread use

around the agency: North American Datum of

1927 (NAD27) and North American Datum of

1983 (NAD83). The latter is a more accurate

description of the earth’s surface and NPS

guidelines recommend that data should be

placed in this datum whenever possible. However, since many agencies still use NAD27,

there is often the practical consideration of

converting large amounts of data obtained from

other sources to NAD83. Again, the most

important concern is that all data to be used

together be in the same datum.

Resolution, Accuracy, and Scale

Other issues pertaining to data include resolution,

accuracy, and scale. Although these terms are not

synonymous, they are often used interchangeably,

sometimes leading to confusion. Resolution refers

to the degree of precision in a data set; that is, how

finely described the data is. In a raster data set,

resolution is the same as the cell size. In a vector

data set, resolution can be thought of in terms of

how closely the shape points in a line or polygon

are spaced. (For a straight line, no more than two

points are needed to describe it precisely.)

Figure 3. A large scanning device converts map information to

digital form. (USGS, 1995)

Figure 4. Digitizing converts map information to digital form

using a hand-held mouse. (USGS, 1995)
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Accuracy describes how close a feature in a data

set is to its real location on the ground. This is

easier to do with vector data than with raster data.

Because raster data is not feature-based, it is often

difficult to discern errors in spatial accuracy from

errors in attribute accuracy unless the entire grid

has been shifted, or rotated from its true location.

Finally, scale is a nearly meaningless term when

applied to digital data storage. Digital data is

essentially scaleless until it is displayed, and even

then its display scale can be easily changed. When

performing spatial analysis or creating cartographic output, the most important considerations are the resolution and accuracy of the

data. Data presented at too low a resolution will

appear crude and blocky when displayed at a

large scale. Since cultural landscape management

often deals with small areas displayed at large

scales, it is often necessary to have very high

resolution data.

A good source for information about the suitability of a data set for a particular need is the

layer’s metadata. Metadata is information about

data. It should include such things as the source

of the data, estimated accuracy, and time from

which the data was collected. Metadata can be

stored in many forms, ranging from a simple text

file for an entire data layer to complex attribute

fields describing each feature in a layer.

Hardware and Software

When the NPS began heavily promoting the use

of GIS in the mid-1980s, there were few powerful software packages available for personal

computers (PCs). Consequently, most parks

turned to workstation computers running the

UNIX operating system. Early GIS software

included GRASS, a package developed by the

United States Army Corps of Engineers, but

most of these systems are now running Arc/Info,

a proprietary package from the Environmental

Systems Research Institute, Inc. (ESRI). The last

few years have seen the rise of GIS software for

PCs, primarily ArcView, another product from

ESRI. Desktop GIS is seen by many in the

agency as the best way to get non-GIS specialists

actively involved in using spatial data for analysis

and mapping. Many opportunities exist for

cultural resource managers to receive training

for desktop GIS. Contact a regional or cluster

GIS coordinator for information.

WHERE TO GO FOR ASSISTANCE

Within the NPS there are many sources for

obtaining further technical assistance related to

GIS. Many parks have staff who are knowledgeable in the use of GIS and who can respond to

inquiries. Many regions and clusters have field

technical support centers that provide GIS

services. In addition, there are regional and

cluster GIS coordinators throughout the NPS

who can provide technical guidance and direct

individuals to appropriate resources. Their

names and phone numbers, along with other

agency-related GIS information, are available

on the NPS GIS world wide web site

(www.nps.gov). For general program information, the national GIS coordinator can be

reached at 303-969-2964. The national GIS

program office also has a cooperative agreement
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with North Carolina State University to provide

consultation and training services. Finally, the

NPS Cultural Resource GIS (CRGIS) Facility of

the Heritage Preservation Services Program in

Washington provides GIS training and data

collection service.

GIS REFERENCES

Adams, Carol. 1990. Visual Protection of National

Parks. In Proceedings of the 2nd International

Symposium on Advanced Technology in Natural

Resource Management.

Allen, Kathleen M., Stanton Green, and Ezra

Zubrow, eds. 1990. Interpreting Space: GIS in

Archeology. London: Taylor and Francis.

Environmental Systems Research Institute. 1993.

Understanding GIS: The Arc/Info Method. New

Jersey: John Wiley and Sons, Inc.

Foster, Mike, and Peter Shand. 1990. Association for Geographic Information Yearbook

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Fotheringham, A.S., and P. Rogerson, eds. 1994.

Spatial Analysis and GIS. London: Taylor and Francis.

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1989. The Accuracy of Spatial Databases.

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________. 1994. Innovations in GIS. London:

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Cousins, eds. 1994. Landscape Ecology and

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The mission of the Department of the Interior is to protect

and provide access to our Nation’s natural and cultural

heritage and honor our trust responsibilities to tribes.

U.S. Department of the Interior

National Park Service

Cultural Resources

Park Historic Structures & Cultural Landscapes