This map service is an information surface representing the shallowest distance to the top of a wet soil layer (the water table) within a soil map unit polygon. The value is the annual minimum as well as the component minimum, so the reported value is the nearest the water table gets to the surface of any significant component in the map unit at any time during the year.
Although there is data for the whole United States for water table depths, not every map unit polygon has a value. Some parts of the United States have more complete coverage of water table depth than others, but values for water table depth depth are still rather piecemeal in character. Quite often, in many places, more than half of the soil polygons have no value at this time. Esri is providing NRCS SSURGO content here without modification except for some cartography and publishing necessary to facilitate esri user access to these data. Of course, esri will continue to update this information as new editions of the SSURGO dataset are published by NRCS.
This map service is a representation of the NRCS SSURGO data table MUAGGATT, field WTDEPANNMIN. The map service will display at scales between 15,000 and 600,000, but the intended scale of the data is 1:24,000. It is based entirely on the US Natural Resources Conservation Service SSURGO polygon dataset, mapped for every part of the United States that has come under survey. Some parts of the United States have not yet been mapped, and in a sense the SSURGO dataset is a seamless collection of individual soil survey maps rather than a single map for the whole United States. As a result, there may be inconsistencies between adjacent surveys because surveys may have been compiled in different decades and with slightly different methods and staff.
The map service is being served to you from a service in the amazon cloud. The map service is published in unprojected geographic space, in coordinate system WGS84. Because the map is published unprojected, it can be projected dynamically to order into the projection of your choosing. This means you can use the map service in any map, not just a "web mercator" projection. This also may mean it will take a second or two to draw your map to order. We welcome your comments on the speed and convenience of this map service.
For best results, this map service is designed to be shown over relief with about 50% transparency. We also recommend for context using the US Hydro Reference Overlay available from arcgis.com here.