Map Reference Basedata
There are two types of reference basedata commonly used in agricultural
GIS mapping systems; aerial imagery, available in various file formats,
and vector data, mostly used in shapefile format. These data are easy
to obtain, however issues such as file format and map projection confound
their use. In the sections below we describe sources of agricultural reference
data and provide the information you need to use it successfully.
Whenever possible we recommend you request any vector (shapefile) data
in geographic coordinates. This is also referred to as "unprojected".
If you receive projected data, the provider must tell you the projection
he or she used.
Much of the reference basedata available is identified by what is known
as "FIPS" codes. To learn more about FIPS state and county codes
visit
this web site.
Due to the size of these datasets, many will be provided as "zip"
compressed files. We recommend you have a copy of WinZip
installed on your computer and be familiar with its use.
If you have any questions, please feel free to e-mail
us. |
Aerial Imagery
Various types of aerial imagery are available from public and private
sources. The biggest challenges users face are obtaining the image in
the correct file format and knowing the projection. Most agricultural
GIS systems require the image to be in the same projection as the map
display for the image to appear.
USDA is the public source for aerial imagery used in agriculture. The
USDA National Agriculture Imagery Program (NAIP)
is responsible for acquiring the aerial imagery used by the USDA agencies
each growing season.
NAIP imagery is available as a single file that covers the entire county,
referred to as Compressed County Mosaics (CCM's), or as individual digital
ortho quarter quads (DOQQ's). The CCM's may range in size from 200 mb
to as large as 850 Mb Their advantage is one CCM image covers an entire
county, where it may take as many as 50 individual DOQQ images to cover
an entire county.
You need to be aware that the NRCS has processed all of the NAIP CCM
images incorrectly, such that the black collar of the image will not appear
totally transparent in a map view (example).
If you only display a single CCM at a time, this is a non-issue. However,
displaying multiple CCM's may result in an unacceptable view. You may
purchase NAIP imagery from MapShots that has
been re-processed to eliminate this problem.
To learn more about the NAIP imagery, please refer to the FSA
FAQ's. |
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NAIP CCM imagery should be available from your local USDA Service Center.
FSA staff may refer to this generically as "Mr. SID" imagery.
The NAIP imagery for your area will be projected in the NAD 83 datum
and be provided in the UTM
zone appropriate for your area.
The NAIP CCM imagery file set contains several files, only one of which
is an actual image file. The image file is identified with a .sid file
extension and that is the file you need.
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NAIP imagery is available from the FSA
Aerial Photography Field Office (APFO) web site. The APFO charges
$50 per county for data ordered from them. The NAIP imagery file sets
contains several files, only one of which is an actual image file. The
image file is identified with a Sid file extension.
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| NRCS Spatial Data Gateway | |
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MapShots has two versions of county mosaics available. The first version
is assembled from TerraServer
image tiles. However, this imagery may be several years old. This imagery
is available in .ecw file format and may be ordered from our Imagery
Order page at a cost of $10 per county.
The second version is NAIP imagery we have obtained from the APFO.
The imagery is 2003 or newer, natural color, and in most cases is 1
meter resolution. This imagery is JPeg 2000 format and has been reprocessed
to eliminate the NRCS transparent collar problem when displaying multiple
images in the same view. This imagery may be ordered from our Imagery
Order page at a cost of $25 per county.
Note: You may contact
us directly to order large quantities of imagery.
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| Other Third-party vendors | |
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| Many third-party vendors can supply aerial imagery.
The preferred file formats are ERMapper (.ecw) and MrSID (Sid). Acceptable,
but less desired are .tif, .jpg and .bmp file formats. The vendor must
tell you the projection of the imagery they are supplying.
Soil Types
Soil type data is available for most counties in the U.S. SSURGO digital
soil surveys contain a multitude of information. However, most of the
information is of little use for agricultural purposes. Typical users
only utilize the soil polygons containing the map unit symbol (MUSYM).
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| Digital soil surveys may be requested
from the local USDA NRCS office. You should request the county spatial
SSURGO data in shapefile format, using geographic coordinates. |
| NRCS Spatial Data Gateway | |
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Digital soil surveys may be requested from the NRCS
Spatial Data Gateway web site. You will be provided with a link
to download a zip file containing the county soils data. The zip file
may contain in excess of 35 individual files. The files containing the
map unit symbol will be named as follows; 'soilmu_a_??###', where ??
is the state abbreviation and ### is the county number.
 How
to request soil surveys from the NRCS Spatial Data Gateway
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Digital soil surveys may also be requested
from the NRCS
Soil Data Mart web site. You should select the county spatial SSURGO
data in shapefile format, specifying geographic coordinates. |
| Other Third-party vendors | |
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| In some areas third-party vendors may
make digital soils data available. It should be requested in shapefile
format, using geographic coordinates. |
Common Land Unit
The USDA FSA has converted most paper-based maps to a digital GIS format.
The CLU typically corresponds to an individual grower's field, as recorded
by FSA. A status
map of CLU data is available. The CLU data is compatible with any
GIS software.
Note: As of May 2008 CLU data is no longer available to the general public. |
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| The local FSA office can provide individual
producer's CLU data. The data will be provided in shapefile format. The
user should request that the shapefile be projected in geographic coordinates. |
TIGER
The US Census Bureau produces data referred to as TIGER (Topological
Integrated Geographic Encoded Referencing) data. TIGER datasets contain
roads and waterway line maps, which are valuable for agricultural use.
However, the full set of TIGER data is cumbersome to work with. MapShots
has made available a modified
set of TIGER data that has all of the non-ag specific data removed.
The data is available from the MapShots TIGER
download page. |
