New attributes in GLIMS

[fmaussion]

I'll leave this here for now, and we can expand later.

To describe glaciers, GLIMS currently "only" has the primeclass attribute, which is the primary classification according to the WGMS:

It must be noted that this attributed is very poorly populated. As of today in RGI7:

category	number
0	274199
2	3
3	70
4	6
6	124
7	27
10	67

I don't know what category 10 is, but is appears in the Bliss et al inventory for Antarctica.

One of the most used attributes in RGI6 is whether the glacier is water terminating, lake terminating, etc. This needs to be added. Whether the glacier is shelf terminating is also another discussion to have.

[fmaussion]

This needs to be revisited based on the final choices made by RGI7 - to follow...