This is a matplotlib/python implementation (the original is in Perl)
The heatmap uses the file size of each tile, which should give a good measure of how much real data there is in a tile. Red areas have lots of data, green areas less, and blue the least.
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.