GeoPackage is an OGC format for vector, tiled and raster data, plus associated metadata, built on top of SQLite. It is described as the modern alternative to formats like SDTS and Shapefile.
GeoPackage is a SQLite database schema. It has the performance of a spatial database along with the convenience of a file-based data set that can be emailed, shared on a USB drive or burned to a DVD. It is intended to facilitate widespread adoption and use of a single simple file format by both commercial and open-source software applications — on enterprise production platforms as well as mobile hand-held devices.
The GeoPackage specification describes a set of conventions for storing the following within an SQLite database:
- Vector features
- Tile matrix sets of imagery (not necessarily in Web Mercator, not necessarily with square tiles, and not necessarily power-of-two zoom) and raster maps at various scales
http://www.ogcnetwork.net/geopackage is a good starting point for the general content.
The OGC GeoPackage standards working group charter is at http://www.opengeospatial.org/projects/groups/geopackageswg
You can contribute to the specification on its Github repository.