Desktop Mapping Resources for Stewardship Site Assessment
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A variety of mapping tools and GIS datasets can be combined to assess site conditions prior to a site visit. Because most data sources are flawed and provide an imprecise view of actual field conditions, combining multiple information sources increases the quality of assessment. By layering all available sources of evidence, an analyst is better able to view the range of possible site conditions, and use a site visit to develop a more precise assessment. Site assessment combines analysis of Landform with consideration of Water Management goals, the presence of Salmon and other wildlife populations, as well as the presence and effects of Transportation infrastructure, and in many cases Agricultural land use. The focus on this page is to identify specific resources that support systematic Site Scale assessment in the USA.
A variety of map data are used to characterize a site. Review of map data ultimately lead to some presumptions about the character and history of a site, and a set of questions that are carried into the field. Field observation can then be used to validate and refine map observations.
Field Map Strategy
I like all field maps to use the same grid and property boundaries. Grid overlays can be very light as they are only used occasionally for orienteering, and for cross registration between different maps. Property boundaries for the subject property can be more prominent. For a detailed site assessment I generally like to go into the field having three maps available:
- Water Flow/Topographic Map - I use a light hillshade augmented by one-foot contour lines for the background (lower resolution if there are lots of steep slopes). Contours need not be labelled but having every 5th line heavier in weight allows for better orientation. I like to overlap stream lines, wetlands, and any data that I have on flow concentration and natural depressions, along with hydric soils. Much of this can be accomplished on the fly with County Mapping Tools. However like to develop flow concentration and depression data in GIS for areas I work in because they provide invaluable information for predicting soil moisture that augments the interpretation of contour lines. Using a multilayered approach provides the maximum information for interpreting field observations and describing areas of greater hydrologic uncertainty (where map information may not adequately describe field conditions). In particular, ditches and culverts are poorly described in map data, and may dramatically affect actual site hydrology.
- Aerial Photograph with Infrastructure - High resolution and unobscured aerial photography provides the best information about land cover, so I like to map known roads but otherwise keep my aerial photos clean, except a light grid for orienteering and cross registration of supporting maps.
- The Soil Map - To keep other maps uncluttered I like to have a soil map, with a transparent soil layer draped on an aerial photo and color coded by soil series. If the site is large and complex, I will use color families (warm vs. cold colors) to describe different soil parent material. For a simple site, a Web Soil Survey printout with marginalia is sufficient.
The On-Line Mappers
Washington State
- Salmonscape provides NHD hydrology, as well as fish distribution data, and state-mapped fish passage barriers
- County Mapping Tools - Mapping portals managed by County governments provide the most field tested stream layers, wetland layers, and may include other state and federal data. They may also serve high resolution local aerial photography better than
USA National
- Web Soil Survey provides the best analytical tool for soils, but no other data.
- Google Earth Pro - Googles downloadable desktop app provides access to time-series aerial photography that can capture
The GIS Data Sets
Washington State
- Washington LiDAR Portal -
- WDFW Fish Distribution Dataset
- WDNR Soil Data
- High Resolution Aerial Imagery Change Detection - WDFW is developing high resolution land cover based on aerial photo interpretation, however these large data sets are not yet available on-line.
National
- National Agriculture Imagery Program - NAIP provides medium resolution aerial photography every 2 years for most of the United States, but the data are laborious to download.
- National Hydrologic Dataset - NHP provides stream lines and water bodies at a national scale, divided by HUC
- C-CAP - The NOAA C-CAP program provides low resolution land cover in 30m blocks. Some areas are being prototyped for a national high resolution landcover program.
