Hi Evan,

There are several ways to archive web tiles and it depends on your level of technical competency and the archive format you want to use. At the higher end of technical you can use GDAL and some scripts to extract the data and reconstitute as a z/x/y folder structure. There is also some java-based software (WIN, OsX, Linux) such as MOBAC and SAS Planet that facilitate the scraping and formatting. Both have similar functionality in that you create a simple script that points to web tile service, you create an area of interest, select the zoom levels you would like, download and then format into a storage format such as MBTILES or the existing folder structure.

MOBAC is easier to use and has pre-made scripts for common open services such as Open Street Maps and Open Topo Map and it relatively easy to format an XML file to point to an appropriate service. SAS Planet is slightly more complex (but does offer more functionality and export functions). Please do note that in SAS Planet there are many sources (links to web tile servers) that are quite likely in breach of the relevant copyright restrictions of the country concerned, so it would pay to do some research beforehand.

The key issue is size. Archiving a complete tile server such as Open Street Map to zoom lvl 19 would be over 1.3 TB. Each zoom level you add is 4 times the size of the previous one. We recently tiled the Natural resources Canada Toporama topographic sheets and that was in excess of 64gb. Then there is the decision of which archive format. I much prefer MBTILES and/or GeoPackage rather than folder-based Z/X/Z and similar. It is much easier to manage encapsulated file formats and utilise them in both web and GIS software. It is also reasonably straightforward to make the archives accessible via web browsers using simple HTML/JS templates.

In terms of metadata some services will already have this available, especially WMS and WMTS based servers. Most tiles services do come with some form of JSON file (or it can be generated easily enough).

If you want to experiment with MOBAC and/or SAS Planet drop me an email I can send you scripts for Natural Resources Canada services (https://www.nrcan.gc.ca/earth-sciences/geography/topographic-information/web-services/17216).

Cheers,

Greg Lauer
East View Geospatial, Inc.
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