What Does This Application Do?
The Series Extent Explorer application can be used to quickly display and compare the approximate geographic distribution of up to five soil series. Data are sourced from a snapshot of the SSURGO database
, last synced February 2017.
Geographic extent and acreage estimates include soils similar to the queried series. For example, when querying "Marpa," data from "Marpa variant," "Marpa taxadjunct," and "Marpa family" would also be included in the resulting map and acreage estimate.
A Quick Note on USDA-NRCS Soil Survey Data
USDA-NRCS soil survey data are currently packaged as a collection of linked spatial and tabular information. Spatial data (e.g. map unit polygons) typically have several associated components (commonly soil series), each with its own set of soil properties and interpretations. Since component data may be used within many different map units, the collection of polygons associated with any given soil series may be very large and complex. For example, the Marpa series is found within 1,257 polygons having a combined area of 244,460 acres and 293,050 vertices. Displaying this level of detail on a regional to national-scale map is generally not very efficient.
How Are Series Extent Acreage Values Calculated?
Acreages are tabulated by soil series using the following formula:
acreage = ∑(polygon_areai * comp_pcti / 100)
is the area of a map unit polygon containing the queried series and comp_pcti
is the corresponding component percentage.
What Do the Boxes Represent?
The generalized soil series distribution maps displayed by the Series Extent Explorer application represent a compromise between map complexity and geographic extent. Soil series with a vast extent are generalized (e.g. San Joaquin, Drummer, Rizno, Cecil, etc.) much more aggressively than series with lesser extent (e.g. Pardee, Amador, Pashua, etc.). Generalization is performed in three steps:
- Collect bounding-boxes associated with each map unit polygon that contains the queried soil series as a major component.
- Geometrically merge all bounding-boxes.
- Snap vertices of the merged bounding-boxes to a coarsened grid, with grid size adjusted according to the total mapped area of the queried soil series:
|Mapped Acres||Snapping Tolerance|
|x < 10,000||0.0001 decimal degrees|
|10,000 ≤ x < 100,000||0.001 decimal degrees|
|x ≥ 100,000||0.01 decimal degrees|
In the figure below, select map units having the Marpa soil series as a major component are shown by the filled blue polygons, merged bounding boxes are shown by the dashed black lines, and the generalized series extent is shown by the red lines. A snapping tolerance of 0.01 decimal degrees was used for the generalized series extent polygons.