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.
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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 re-processed 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 directy 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.
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| 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. |
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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.
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Common Land Unit
The USDA FSA is in the process of converting all 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.
CLU data obtained publicly only contains a calculated area
for each CLU polygon and consists of the entire county. Individual
producers can sign a release form so their service providers
can obtain their personal CLU data. These CLU data will contain
full FSA farm and tract identification, but be limited to
the individual producer's land that he or she operates.
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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.
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| NRCS Spatial Data Gateway | |
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County CLU data may be requested from the
NRCS
Spatial Data Gateway web site. You should request the
CLU data in shapefile format, using 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.
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