Updating the airport database
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(1) Download timezone shapefile

Pick the latest timezones.shapefile.zip from
https://github.com/evansiroky/timezone-boundary-builder/releases

Extract the zip file into this folder.

(2) Generate timezone lookup map

Open timezones.qgs in QGIS. Select "Project" > "Layouts" > "timezone_lookup_map" and then
"Layout" > "Export as Image". Choose "timezones.png" in this folder, 2400dpi, enable
"Generate world file" and *disable* anti-aliasing.

(3) Run the code generator

Run `make rebuild-knowledgedb` in the build dir of this folder.
