Add How to guide for GADM data sets

[Esteban82]

I made this how to guide to download and use GADM data.

I choose to download KMZ files (not geopackage as Joaquim did with Julia) because they were slightly smaller.

Maybe it would good to modify the script to store the data in a directory where all the GMT programs can found it (not in the current directory).

[Esteban82]

Related to GenericMappingTools/dcw-gmt#30 (comment)

[anbj]

Could you give me a quick intro on the gmt-examples repo;

• is it hosted somewhere, or does it have to be downloaded and built locally?
• Is there an entry point/link in the gmt docs?

[joa-quim]

KMZ may be slightly smaller but it will be slower to process as it will make two copies in ascii. One from kmz to kml and another from kml to .gmt. And the second conversion implies that ogr2ogr will have to parse a big xml ascii file to convert it to .gmt

[Esteban82]

The idea is to add examples in another repository (this one) and not in the main one (where the code is).

• is it hosted somewhere, or does it have to be downloaded and built locally?

https://www.generic-mapping-tools.org/gmt-examples/

• Is there an entry point/link in the gmt docs?

We should add one.

[Esteban82]

KMZ may be slightly smaller but it will be slower to process as it will make two copies in ascii. One from kmz to kml and another from kml to .gmt. And the second conversion implies that ogr2ogr will have to parse a big xml ascii file to convert it to .gmt

Ok, I will try to update the script to use geopackage instead.

[Esteban82]

I checked and I don't think that it is a good idea to download the gpkg files. All the levels are together in the same file. There are some examples of big files (e.g. IND 447 MB, GBR 412 M).
To be clear, in the case of GBR you will download up to level 4 even if you want to plot only level 1.

I think it is better to use KMZ (or JSON aslo) where the data is split in levels, so you directly will download the level that you want to use.

[joa-quim]

OK, good to know that.

[Esteban82]

Is this ready for approval? Or are there any comments?

[seisman]

Need to update the gallery after #28

[Esteban82]

I am bit confused about how to do it. I will cancel this PR and make a new one.

[seisman]

You don't need to open a separate PR #29, just need to update the following lines:

Suggested change

	.. cssclass:: gmtgallery
	- .. image:: _images/7dd36e07258e1015a0673dea4e472db1.png
	:target: gallery/maps/gadm.html
	:width: 80%
	:align: center
	:doc:`gallery/maps/gadm`
	.. grid:: 2 3 3 4
	.. grid-item-card:: :doc:`gallery/maps/gadm`
	:padding: 1
	:link-type: doc
	:link: gallery/maps/gadm
	.. image:: _images/7dd36e07258e1015a0673dea4e472db1.png