What you probably didn’t know about USGS Topos

Many of the nation-wide vector datasets have their origin in USGS Topos. TIGER Line files were initially digitized from USGS Topo sheets, and have been updated by the Census since this time.

DRGs were created in the late 1990s by scanning in all of the USGS Topographic sheets, and are commonly used for illustration because they are raster and not vector. Although they are grainy and aliased, they are still commonly used because there is no updated standard map set available in nation-wide coverage.

Recently, an organization called the W.E. Upjohn Center for the Study of Geographical Change has re-scanned the entire US database of topographic maps using scanning technology designed to make GIS data from paper maps. So even though the Topos are accurate to only +/- 40 feet, the 1:24,000 scale digital data created from these maps lines up impeccably with 1:12,000 scale imagery. This is largely due to the fact that these topos were actually field checked up until the 1980s, when USGS started making updates from air photos without field checking. In fact, the USGS was the first organization to ‘crowd-source’ data, through a program in the 1980s called Earth Sciences Volunteers.

This updated DRG series is called US Authoritative Topos, and can be purchased for the desktop environment at www.upjohncenter.org and for use in the mobile environment through the Avenza pdf maps storefront – tried and tested for the iPhone/iPad environment, and in beta for Android. The cool thing about this map app is that it allows you to store the map locally, so when you’re out in the field you don’t need to use your data – just have your GPS enabled. AND you get access to physical features and contours which are nice when you’re exploring – can’t get that info from Google or Bing. When I was at Pictured Rocks last summer we had few daylight hours to catch a short hike, and wanted to check out Munising Falls. Google Maps directed us to places that had “Munising Falls” listed in their website, but not the physical location of the trailhead. The mobile Topo got us close enough that we could follow the infamous “brown” park signs to catch the falls before sundown.

 

Margaret Spyker

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