The Aerial Photo layer is based on 1m resolution grayscale USGS orthophotos. A digital orthophoto quadrangle (DOQ) is a computer-generated image of an aerial photograph in which image displacement caused by terrain relief and camera tilts has been removed. It combines the image characteristics of a photograph with the geometric qualities of a map.

All the orthophotos that cover Pennsylvania were projected from UTM to Albers NAD 83. The projected photos were then combined into a single statewide ArcSDE raster mosaic stored in Sql Server. This raster layer is then displayed in SoilMap. Each quarter-quad is a photo, with a total of over 3200 orthophotos for Pennsylvania.

The dates of the photos vary from 1993 - 1999. The date of a photo can be determined by using the Spot Analysis Tool. Click on the tool and then click on the map. The report that appears will show the date of the photo for the quarter-quad that was clicked. The Aerial Photos layer is only visible at map scales less than 1:100,000.

For More Information - Read the USGS DOQ fact sheet , visit the DOQ Home Page or the USGS Guide to DOQ Data. To download DOQQ data for Pennsylvania, visit PASDA.

Note: All SoilMap source data has been projected to an Albers Conical Equal Area projection with the following parameters.

PROJCS["Albers Conical Equal Area",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Albers"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-78.0],PARAMETER["Standard_Parallel_1",40.0],PARAMETER["Standard_Parallel_2",42.0],PARAMETER["Latitude_Of_Origin",39.0],UNIT["Meter",1.0]]

The data and documentation on SoilMap are provided 'as is' and the User assumes the entire risk as to their quality and performance. SoilMap source data was produced at a variety of scales and may not be suitable for use at larger scales.