Q How do I cite this data in a
report?
A The way to cite the digital data is like
citing the published soil survey. Here is some examples.
For a published copy
<Author>. <date of issuance>. Soil Survey for <County, State>. United States Department of Agriculture, Soil Conservation Service. U.S. Gov't Printing Off. pp. <###>.
NOTE: USDA-SCS changed their name after all the Pennsylvania published soil surveys were done. Any new publications will be the Natural Resources Conservation Service.
For a digital copy from the MC&DC/PASDA web site.
Pennsylvania Map Compilation and Digitizing Center Staff. <date of dataset>. Interim electronic spatial and tabular data of the Soil Survey for <County, State>. Version <#.#>. United States Department of Agriculture, Natural Resources Conservation Service. Available URL: "http://mcdc.cas.psu.edu/" University Park, PA.
NOTE: All the data on our site is an interim copy subject to change before it is SSURGO certified, so therefore the difference with the bottom listing.
For our digital SSURGO certified copy found at the Soil Data Mart site.
Soil Survey Staff. <date of dataset download>. Spatial and tabular data of the Soil Survey for <County, State>. United States Department of Agriculture, Natural Resources Conservation Service. Available URL: "http://soildatamartnrcs.usda.gov/" Fort Worth, TX.
For referncing the Web Soil Survey, an interactive web-based soil survey data exchange system:
Soil Survey Staff. Web Soil Survey of <<County or Area, State>>. Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey [Online WWW]. Available URL: "http://websoilsurvey.nrcs.usda.gov/app/" [Accessed <<Access Date>>].
Q
How accurate is the digital soils data?
A The digital data must
maintain a 0.01 inch tolerance from the source compilation document that
was scanned at 250 dpi. This works out to about one line width drawn from
a 0.5 mm pencil. The digital data must maintain a 40 ft/12 m tolerance
from its actual placement on the aerial photographic base maps typically
used for modern soil survey publications.(National Soil Survey Handbook,
Part 647, Sec 7; Metadata) (Tim Craul, Soil Scientist, SSURGO Specialist)
Q How accurate is the soil survey
data?
A The soil survey data is accurate for
the mapping model that was used to design the map units and their spatial
location. Field soil scientist's have long used a mental mapping model
that has been designed with the scale of mapping, complexity of the survey
area, and the typical uses of the soil survey in mind. This model is refined
through field investigations until a firm understanding is achieved of
the soil-landscape relationships. The soil-landscape relationships are
then applied to the survey area. The problem with the mental mapping model
is that lay persons not versed in field soil mapping will have a hard
time understanding the reasons for placement of the map units. (Tim Craul,
Soil Scientist, SSURGO Specialist)
Q Why does the digital data not match the soil survey
book that I have?
A There are several counties that have been
updated by field soil scientists to modernize the soil survey. These counties
are Adams, Berks, Bucks, Chester, Franklin, Fulton, Northampton, Lehigh,
Pike, Westmoreland and York. Since they have been updated to reflect new
land uses, technology, and changes in how we interpret soils for a widening
variety of uses, they are different than the "out of date" published
soil survey. Soil surveys only have a life-time of about 20 years where
the requirements of the soil survey users change, as well as our understanding
of how to interpret the soils. Eventually all the counties in Pennsylvania
will be updated to modernize them. (Tim Craul, Soil Scientist, SSURGO
Specialist)
Q What are inclusions?
A Inclusions within a soil survey deal with
"other" soil types found within each map unit. For example,
a Hagerstown silt loam, 3 to 8 percent slopes can have up to 25 percent
of the map unit made up of soils other than Hagerstown. These soils can
be wetter, shallower to hard limestone bedrock, or even soils that encroach
from surrounding soil map units. (Also see Metadata for explanation of
Consociations, Complexes, and Associations)
For more information dealing with soil survey procedures and accuracy
see the National Soil Survey Website. (Tim Craul, Soil Scientist, SSURGO
Specialist)
Q How are errors rectified?
A Errors in the digital data are typically
found during the quality control phase of the digital procedure. The more
likely errors are ones we found in the published soil survey that we have
to correct. This is done by trained USDA-NRCS soil scientist who research
each error, make a decision, and document that decision based on their
research and experience. Corrections to the uncertified data is relatively
easy, the certified data require re-certification of the databases. (Tim
Craul, Soil Scientist, SSURGO Specialist)
Q Why are there some areas where the soils layer waters
do not match the water shown on the digital orthophotograph?
A Certain counties were compiled using an earlier
vintage of orthophotograph where the waters changed due to seasonal changes
in lake, pond, and stream height. There might also be changes in water
courses in streams and rivers over time that have occurred in-between
the time of the orthophoto used for the soils compilation and newer digital
orthophotos. Within the metadata, the vintage of the base map used to
compile the soils is stated under "Lineage". This will help
the end-user to determine the time period of the data. (Tim Craul, Soil
Scientist, SSURGO Specialist)
Q Why do certain counties soils layer not match the
adjacent county's soils layer?
A In the digital process there are many steps.
One of the later steps in the digital soils data evolution is the joining
between counties. If you notice on the Digital Status Map, there are counties
highlighted in light blue. Typically, these counties have not yet be joined
to surrounding data. SSURGO certification requires that there is an acceptable
join between soil mapping units, an exact line for line join between soil
delineations, and a common boundary. In order to accomplish this task
a soil scientist must complete this join, and document any changes to
the "Official" Soil Survey. Edgematching takes two weeks per
county join on the average. If there are four counties joining one soils
data set, it takes 2 months to complete the county join. We are working
toward a seamless soils coverage, but everything does take some time.
(Tim Craul, Soil Scientist, SSURGO Specialist)
Q
What is SSURGO?
A SSURGO stands for Soil Survey Geospatial
data. SSURGO data is spatial data from the soil survey area, typically
at either 1:12,000 or 1:24,000 scale of mapping. There are two other databases,
NATSGO and STATSGO. NATSGO is the nation-wide soils database that is very
generalized with a very small scale of mapping. STATSGO is the soils database
for a whole state. None of these spatial data bases should be used for
site-specific requirements. The soil survey data is strictly for general
planning purposes, not to be used for areas smaller than the minimum delineation
of mapping. (See Metadata) (Tim Craul, Soil Scientist, SSURGO Specialist)
Q
What does SSURGO Certification mean?
A Certification of SSURGO soils data
requires a multilevel review of the compilation through digitizing steps.
Once a database has passed all the quality control and quality assurance
procedures, the data is archived at the National Cartographic and Geospatial
Center in Fort Worth, Texas. The archived data is now the "official"
data and should be downloaded from Fort Worth to make sure that you have
the "latest and greatest" data available. (Tim Craul, Soil Scientist,
SSURGO Specialist)
Q What is the digital
soils data that you dispense?
A The data that the Map Compilation
and Digitizing Center distributes is an interim product until the data
has been archived. This data is subject to change and has not gone through
the entire quality review that certified data has gone through. Typically,
we will not release data that has not been at least checked versus the
published soil survey completely. We are trying to at least match the
published soil survey data. In order to certify the data, it must at least
have an acceptable join with adjacent soil survey areas. This causes changes
to be made to the published soil survey; however, documentation dealing
with those changes are maintained with the "official copy" of
the published soil survey and other documents kept within our office.
(Tim Craul, Soil Scientist, SSURGO Specialist)
Q What are the various projections of soil data available
on the web?
A The data contained on the MC&DC
web site that is also linked to PASDA is all in NAD83 datum and UTM Zones
17 and 18. For counties that fall within both zones like Centre and Clinton,
whichever zone the majority of the county falls in is what the zone is
for the entire county. DOQQ's downloaded from PASDA for the majority of
the county will overlay properly. For the DOQQ's that are in the different
zone will not overlay properly. You must re-project the soils to the other
zone for the soils to overlay properly with the DOQQ's. For instance in
Clinton County, Sinnemahoning and Pottersdale DOQQ's will not line up
with the soils because they are in UTM zone 17 and Clinton Co. was archived
on PASDA in UTM zone 18.
The SSURGO Certified data archived on the SOIL DATA MART site at the National
Cartographic Center (NCG) has several projections and datums that can
be user defined before download. The metadata associated for each county
is written for a quad-by-quad basis for the survey area. (Tim Craul, Soil
Scientist, SSURGO Specialist)
Q What data do I download for the SOIL DATA MARTsite?
A If you are using an ESRI product
I suggest that you download the shapefile of the data. This is closest
to the archived data source and has not been converted to another output
file format, ie. coverage or Arc exchange format. There are several files
that come with the data: smu_a_PAXXX is the soil area layers, the spatial
data; ssf_l_PAXXX which is the special line soil symbols that include
rock escarpments, short steep slopes etc.; ssf_p_PAXX which is the soil
point feature layer that includes wet spots, marsh spots, quarries, gravelly
spots etc.; ssa_a_PAXXX is the boundary of the soil survey area; ssf_t_PAXXX
is the pipe delimited text file describing the special feature symbols.
Do not forget to download the attribute data as well, because without
it all interpretations that can be related spatially can not be accomplished.(Tim
Craul, Soil Scientist, SSURGO Specialist)