Datasets with helpful information everyone should know
Maps.me, osmand support KML files. You can import KML files in these applications to have your required maps in your mobile phones (in online or offline modes).
For example, you can create your own map in Google Maps and export it as a KML file. Be attentive, coordinates should be defined in resulted KML file to show objects!
You can also get KML files from JSON (json -> csv -> kml conversion chain) or from CSV (csv -> kml).
https://www.convertcsv.com/json-to-csv.htm
https://www.convertcsv.com/csv-to-kml.htm
In the child directories prepared datasets for cities in *.json and *.kml formats exist. You can use it to import in your applications that support such formats.