0

Does a database or dataset exist that lists all exact Degrees, Minutes, and Seconds (rounded to nearest decimal) for the continent of South America? What I am seeking is a list of DMS's that covers that entire geography; not just a few specific coordinates, but all of them. Given that each DMS represents ~60 nautical miles apart, the data shouldn't be overly complicated to form. The trouble is, I can't locate the consolidated data anywhere on the web!

2

Outline solution:

  • Get boundary data for all countries in the region (can be downloaded from gadm.org)

  • Loop over all D/M/S on the earth, doing point-in-polygon tests over the boundary data from step 1 - this can be done using Python, R, Java or C or lots of other programming languages.

  • Keep those D/M/S values that are inside the boundaries.

How many points would you expect? The whole earth is 360 degrees round and 180 degrees north-south, so thats 360*60*60 * 180*60*60 = 8.4 x 10^11 points. South America is maybe 1/10 of the planet, so that's about 10^10 points - a few billion.

You'll end up with a table of a few billion points. I'm not sure how that would be useful, but that's how you'd do it.

  • I opted to use QGIS3 with the imported GADM.org boundary layer for the Earth. With the boundary layer correctly placed in the "layers" section of QGIS3, I then created a custom polygon shape. From there, I attempted to use the "Count Points in Polygon..." feature followed by the "Open Attribute Table" to collect the desired D/M/S values. Unfortunately, the resulting table indicates that there are zero points present within the polygon shape. – ScienceGuy Oct 28 '18 at 20:19
  • Did you first create a grid of DMS points over your study area? – Spacedman Oct 28 '18 at 20:46
  • I did not. The reason being is that I don't know the D/M/S points. The collection of the points was intended to come from the GADM.org data, or so I thought. How can I create a grid of points if the points are unknown at the time of capture? – ScienceGuy Oct 28 '18 at 22:11
  • In my outline you first generate a grid of DMS points over the whole earth. You can also generate a grid of points that span a vector layer in QGIS with one of the vector processing algorithms – Spacedman Oct 28 '18 at 23:01
  • Thank you for the further replies, Spacedman. I followed that outline (which was very much appreciated), but I'm still unclear on how to access the DMS points with which to generate the grid--the grid part I understand, as well as all points thereafter. How does one present/collect (for lack of a better word) the DMS points from the GADM.org data in the first place? – ScienceGuy Oct 29 '18 at 0:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.