Test serialization of coordinates

[xivk]

Test the storage of coordinates and the resolution needed for different zoom levels.

When using x-bytes for lat/lon:

• 2bytes gives 256 resolution per tile.
• 3bytes gives 4096 resolution per tile.
• 4bytes gives 65536 resolution per tile.

We need to figure out what resolution is ok for zoom levels:

• 14
• 12
• 10