Re: geographic plotting

This MAY answer your question. I've done this sort of visualization
before by grabbing raster map images from any tile server (openstreetmap
for instance), and plotting data on top of the image.

Script to

- download the tiles you want
- stitch them together into one image you will be overlaying
- generate a template gnuplot script to plot this image

is available here:

  https://github.com/dkogan/osmgnuplot

The script plots lat/lon on one set of axes, and image pixel coords on
the other set. The mapping isn't linear, and the generated script
handles this. So you can plot your overlay with latlon coords. Works
great. Some (very simple) results in these blog posts:

  http://notes.secretsauce.net/notes/2017/09/25_pole-of-road-inaccessibility-of-the-contiguous-us.html

  http://notes.secretsauce.net/notes/2015/08/16_least-convenient-location-in-los-angeles-from-koreatown.html