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If I understand your proposal, tiles are square in pixels, and in coordinate extent

How is that going to work with anything except spherical mercator?

Should the SRID be stored as asimple integer or should it include the Authority Name?

Currently, there is no way to specify the origin of the tileset. This assumes that the tileset origin is the same as the SRS/CRS origin.

Should we allow for overriding the origin of the tileset? Many of the tile services allow setting a different origin than the SRS/CRS.

OpenStreetMap XYZ Tiles are widely used. Should this spec be able to support the OSM XYZ schema? It would require a few modifications, but may be worth it.

• All setting of tileset origin
• Change 0,0 tile to be upper left corner tile

References
http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames

Since some target platforms have a file size limitation, i.e. Android 2.2 and FAT32 SD Cards, there needs to be an extensible way to store tile data.

Two current options are:

1. Store in uncompressed zip files
   * Pro: Work with existing tools, uncompressed files don't have to be extracted first, zip standard includes file spanning, individual tile files can be stored without modification
   * Con: Library support on platforms unknown, file spanning support unknown
2. Store in protobuf format
   * Pro: Simple format, proven with OSM PBF format
   * Con: Requires writing tools to generate
3. Other suggestions?

Storing individual tile files on disk is a non-starter. Transfer times increase exponentially with the number of files being transferred. Too easy to miss files during transfer. Results in wasted disk space on some file systems due to block size.