Have you ever noticed that the distances computed by digital mapping tools are substantially different from paper maps and guidebooks of the same area?
I’ve been planning a 200 mile backpacking trip and the digital mapping tools I’ve been using, Caltopo and TOPO!, underestimate the mileage by 15% or nearly 30 miles over the course of my journey. That’s a significant difference, equivalent to two entire days of hiking and food.
What causes these discrepancies and which version of the route should I trust?
Good question. I’m not sure I can give you a definitive answer.
Here’s a simple example. I’ve carefully drawn a line from Imp Shelter to Mount Moriah in the picture below using Caltopo. I zoomed in when I drew the line to make sure that I captured every twist and turn of the trail shown on the digital map. Caltopo reports that this line, which is a segment of the Appalachian Trail, is 1.39 miles long. But I have a paper map and two guidebooks that say it’s 2.3 miles in length. Topo!, another digital mapping program, says the distance is 1.53 miles in length. Both digital tools are significantly under-reporting the length of this trail segment.
One possible explanation is that the map data in the digital tools is historically out of synch with the paper maps and guidebooks. Trails can be very dynamic: they’re often rerouted due to erosion, landowner disputes, or boundary changes.
But, these digital mapping tools are way off and the trail depicted hasn’t moved that much in the past 50 years.
Surely, I can’t be the only person experiencing this issue. Please enlighten me. Why is this happening?