There are many advantages of GPS-captured data over remote imagery
Detect primitive roads
Highways and other paved roads are easily extracted from imagery. These do not represent the most common types of routes in this district. Primitive dirt and gravel roads and single tracks are often indistinguishable from washes, horse and cow tracks that are lost in the never ending sea of sagebrush. Ground crews may even have difficulty finding these routes until they are immediately upon them. Imagery and other automated data acquisition methods do not find these routes.
Assess route quality
Route conditions and assessments such as trail surface, obstructions and use level can only be made by field observations. A field crew is needed to make these determinations and shoot a GPS-photo that supports these observations.
Data at 1:100k is accurate to only 50.2 meters as per national map accuracy standards. Project data was collected with mapping grade GPS devices and processed for sub-meter accuracy.
Maintain a presence on the public lands
To keep apprised of activities and conditions on the public lands, agency personnel must make regular onsite visits and inspections. This is especially important since the majority of the travel routes in the district are not maintained or assigned to any particular owner (county, federal, private etc).