Precision of Barrington Atlas coordinates

Sources of error

• Base map precision: 1/50"
• Mylar registration: 1/50"
• Feature placement: 1/30"

Sum: 0.073333"

Precision is dependent on map scale, and the Barrington Atlas incorporated maps at 4 different scales. Nominal precision for each scale is as follows:

• Maps at 1:250,000: 465m
• Maps at 1:500,000: 930m
• Maps at 1:1,000,000: 1860m
• Maps at 1:5,000,000: 9310m

Ground Truth

Choma

For what it's worth, compare the BA coordinates for Choma

http://pleiades.stoa.org/places/638803.kml

to the actual dig 1.5 km to the NE. That's ballpark of our nominal error for maps at 1:500K.

Sagalassos

The BA coordinates for Sagalassos

http://pleiades.stoa.org/places/639087.kml

are even closer to the truth, well under a kilometer (also 1:500K source map).

Visualization and Documentation

Going forward, we need to surface these details better for users. On the Google Earth / KML side, it's essential to do this both in textual form and, insofar as possible, an intuitively helpful visual form. The following images illustrate one possible solution for communicating accuracy and precision in Google Earth:

Currently, we look like this:

Maybe we should look like this:

And maybe we should add some accurate but not too jargon-laden text like this: