DRG - Bushkill, PA

http://www.dpi.nsw.gov.au/agriculture/field/pastures-and-rangelands/establishment/clover/part-f---choosing-the-right-sub-clover-v

Digital Raster Graphics (DRGs) is a digital image created from scanning a USGS paper topographic map.  These maps can be useful as backdrops for overlaying other digital data and also for checking errors within existing vector files of such entities as rivers, lakes, or streams.  These maps are scanned at a resolution of 250 dots per inch so they can be used for this accuracy check with other vector files.

The image above is a magnified section of a DRG for Bushkill, PA.  In it, we can see various features such as constant altitude lines, roads, buildings, and bodies of water.  Having maps such as this (that were created from land surveying practices) is extremely important for digital map accuracy.