Open Topo Map	https://a.tile.opentopomap.org/$z/$x/$y.png
Open Street Map	http://tile.openstreetmap.org/$z/$x/$y.png
USGS Topo	https://navigator.er.usgs.gov/tiles/tcr.cgi/$z/$x/$y.png
USGS Imagery	https://navigator.er.usgs.gov/tiles/aerial_Imagery.cgi/$z/$x/$y