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**Geographic Information System (GIS)**

**INFORMATION SHEET**

**May 2008**

-   **What's a Geographic Information System?**

> A Geographic Information System (GIS) describes any automated system
> for spatially managing and analyzing geographic information.
>
> In simplest terms, most everything has a physical location on the face
> of the earth; by default it has a spatial component. GIS is the
> managing, leveraging, and/or virtual display of information about
> things that have a spatial component.
>
> Most but not all geographic data has a projection, which is a
> mathematical attempt to place what is seen on a flat computer screen,
> or printed page, at the coordinates/location of where it really exists
> in the three dimensional world.
>
> GIS is part of a larger field called Geographic Information Science, a
> more overarching, and academic field dealing with the totality of
> hardware, software, geospatial data, and their interactions.

-   **What kinds of data can GIS use?**

> Generally speaking, GIS stores two types of spatial data: Vector
> format data and Raster format data.
>
> Vector data is a coordinate-based data structure commonly used to
> represent linear map features. Each linear feature is represented as a
> list of ordered x,y coordinates. Attributes can be associated with the
> feature. Vector data includes:
>
> 1\. Point features (signs, tractors, grain silos, etc.)
>
> 2\. Line features (roads, fences, sidewalks, etc.)
>
> 3\. Polygon features (fields, land use, wetlands, etc.)
>
> Raster data is data displayed as discrete picture elements (pixels).
> It is a cellular data structure composed of square rows and columns.
> Groups of cells represent features. The value of each cell determines
> the tonal value of the feature. Raster data can include aerial
> photography, scanned images, and any other information displayed and
> stored as pixels.
>
> GIS can also store almost any kind of attribute data. Attribute data
> is data that further describes spatial data. For example, a point
> feature may be a sign, but the attribute data could specify what type
> of sign it is: stop, yield, or speed limit. Attribute data is stored
> in associated tables, text files, or databases. The real power of GIS
> is in accurate attribute data.

-   **For what purposes do people use GIS?**

> 1\. Map the location of things: Mapping where things are located
> assists users in finding geographic features, and in measuring
> distances or transportation routes between features. Visualizing
> locations on a map can assist in decision making.
>
> 2\. Finding patterns: Observing the distribution of features on the
> map can reveal patterns, which can assist in analysis.
>
> 3\. Map densities: Mapping features will display their geographic
> concentration, but in areas with many features it may be difficult to
> determine which areas have a higher concentration than others. A
> density map displays measurements of the number of features, so you
> can clearly see the distribution.
>
> 5\. Map quantities: Quantities are mapped to assist with study
> objectives, or to compare data in different places. This type of map
> can aid with decision making, because it gives an additional level of
> information beyond simply mapping the locations of features.
>
> 6\. Find what's inside something: Mapping quantities or densities in
> specific areas could help to monitor what\'s happening and to take
> specific action. For example, maybe within a particular city district,
> crime is higher than in other districts. This finding could lead
> police to increase patrols.
>
> 7\. Find what's nearby something: Create buffer zones and discover
> what\'s occurring within a set distance of a feature. This type of
> analysis is crucial to environmental planning.
>
> 8\. Map changes: Map changes in a particular area in order to predict
> future conditions, decide on a course of action, or to evaluate the
> results of a previous decision.

-   **How does the Farm Service Agency (FSA) and Aerial Photography
    Field Office (APFO) use GIS?**

> USDA FSA programs help agricultural producers purchase and operate
> farms, stabilize farm income, conserve land and water, and recover
> from the effects of disasters.
>
> In order to determine producer benefits for most FSA program areas,
> FSA must know the specific crop acreage or other land use information.
> Also, for many programs, producers agree to certain provisions on
> their land, such as conservation compliance.
>
> GIS helps FSA staff to more efficiently measure land features by
> allowing computer-generated maps to interact with databases that store
> information about the land (attribute data). This technology gives
> local offices tools to:

1.  Help producers to exercise sensible land stewardship;

2.  Provide quicker, more accurate information for decision-making
    purposes; and

3.  Reduce the amount of time a producer must spend working with local
    FSA staff in order to participate in USDA programs.

> USDA-FSA-APFO helps manage 2 primary datasets:

1.  Aerial Imagery

2.  Common Land Unit (CLU)

> Aerial Imagery, a raster dataset, is the base layer in GIS over which
> other data, such as CLU, which is a vector dataset, are overlaid and
> digitized.
>
> Depending on the purpose of the work, other data layers may also be
> added. The end product is a group of layers that represent real world
> features in the form of a map. GIS allows for much more detailed
> information than is contained in a hard copy map with a color-coded
> legend; the attributes could be used to create an entire series of
> maps. Each GIS layer can store and display vast amounts of
> information, such as soil types, crops, land boundaries, place names,
> and populations.
>
> No matter how vast the GIS database is, it can be queried and
> organized to propagate efficient data management practices. A simple
> GIS query can locate one farm number from thousands, in just seconds.
>
> Further uses of GIS by USDA FSA relate to:

1.  Farm Commodity and Conservation Programs

2.  Farm Loan Programs

3.  Emergency Preparedness

4.  Compliance

-   **What is a CLU used for?**

> The most critical component of GIS for FSA is the development and
> maintenance of the Common Land Unit (CLU). CLU is the smallest land
> unit with a permanent contiguous boundary and land cover; in other
> words, a farm field. USDA FSA digitizes CLU into Geographic
> Information System (GIS) shapefiles (soon to be ArcSDE feature
> classes) and populates associated attribute data.
>
> There are many uses for CLU, including but not limited to:

1.  Providing a link between tabular farm records and a map or image of
    the land;

2.  Using GIS for acreage calculations;

3.  Replacing paper maps with digital images that can be easily updated
    and can produce high quality prints whenever necessary;

4.  Drawing crop boundaries to better define or use with other data,
    such as:

    a.  Crop Patterns

    b.  Subdivisions

    c.  Conservation Plans

5.  Creating a central database for land unit boundaries and linking it
    to customers; and

6.  Speeding up the process for implementing disaster payment and other
    specialized systems.

-   **How do farmers benefit from GIS?**

> GIS technology can help agricultural producers improve production
> history and farm planning through precision agriculture. Producers can
> request copies of USDA imagery, farm and field boundaries, and soils
> data to help them with:
>
> 1\. Planning, such as determining crop planting strategies
>
> 2\. Crop production, such as mapping and monitoring fertilizer and
> herbicide application.

-   **Can I build my own GIS?**

> Yes. All you need to get started is software and data.

-   **Do I have to purchase GIS software?**

> No. Software for basic GIS functionality is free for download; more
> advanced GIS software does come with a substantial associated cost.
>
> For more information on free GIS software and downloads, go to the
> following sites:
>
> <http://software.geocomm.com/viewers/>
>
> <http://gislounge.com/ll/freedataviewers.shtml>
>
> <http://spatialnews.geocomm.com/features/viewers2002/>
>
> This list is provided for convenience; USDA-FSA-APFO does not support
> or endorse these products or services.

-   **Do I have to purchase GIS data?**

> No. There is an abundance of free data, in numerous data warehouses,
> on the web. The key is to having a clear objective in seeking data.
> The Geospatial Data Gateway, at <http://datagateway.nrcs.usda.gov/> ,
> contains a great deal of imagery and vector data available for public
> consumption. Many state governments also have their own
> clearinghouses.

-   **Who do I contact for more information?**

> 1\. For APFO sales and product information, contact USDA-FSA-APFO at
> 2222 W 2300 S, Salt Lake City UT, 84119-2020, call 801-844-2922, or
> visit [www.apfo.usda.gov]{.underline}.
>
> 2\. For further information on GIS, contact GIS Specialists at APFO:
> Louise Mathews, 801-844-2934; or Nathan Pugh, 801-844-2927