Improve description of link tables #83
Description
I feel that the description of the link tables may benefit from a bit more precision about what each column represents. I also would like to correct the equivalence made between n:n relations and clusters, which are in fact not equivalent.
So the current text (https://www.glims.org/rgi_user_guide/products/glacier_product.html?highlight=_links#product-files):
A list of overlapping outline pairs between RGI 7.0 and RGI 6.0 describing 1:1, 1:n, n:1 or n:n relationships as well as the overlapping area between them. For example, a perfect match between an RGI 7.0 and RGI 6.0 outline results in a 1:1 relation with 100% area match in both. If a single RGI 6.0 outline was divided into two glaciers for RGI 7.0, a 2:1 relationship (a cluster) would result with two lines in the table with twice 50% area match in RGI 6.0 and twice 100% match in RGI 7.0. In more complex cases the matches are not always perfect and the relationships less straightforward, for example when an outline was remapped.
Could become something like:
A list of all overlaps (greater than 200 m2) between RGI 7.0 (rgi7_id) and RGI 6.0 (rgi6_id) glacier outlines. The overlap area (overlap_area_km2) is divided by the area of the original outlines to also provide area fractions for RGI 7 and RGI 6 (rgi7_area_fraction and rgi6_area_fraction), respectively. Columns n_rgi7 and n_rgi6 indicate whether each overlap is isolated (a 1:1 relation) or part of a more complex 1:n, n:1, or n:n relation. For example, a perfect match between an RGI 7 and RGI 6 outline results in a 1:1 relation with overlap area fractions of 1. If an RGI 6 outline is divided into two outlines (of equal area) in RGI 7, the table will contain two rows with n_rgi6: 1, n_rgi7: 2, rgi6_area_fraction: 0.5, rgi7_area_fraction: 1. Often the relation between RGI7 and RGI6 is more complex, for example when an outline was remapped in RGI 7 and partially overlaps many in RGI 6.
Note that n_rgi7 and n_rgi6 only count direct relatives – that is, the total number of RGI 7 outlines overlapping rgi6_id and the total number of RGI 6 outlines overlapping rgi7_id. Column cluster_id groups together all overlapping RGI 6 and RGI 7 outlines such that each cluster does not overlap any other cluster.
Or probably better with the help of a table:
A list of all overlaps (greater than 200 m2) between pairs of RGI 7.0 and RGI 6.0 glacier outlines, described by the following columns:
| Column | Type | Description |
|---|---|---|
rgi7_id |
string |
RGI 6.0 outline |
rgi6_id |
string |
RGI 7.0 outline |
overlap_area_km2 |
number |
Overlap area in km2 |
rgi7_area_fraction |
number |
Overlap area (overlap_area_km2) divided by the area of the RGI 7.0 outline (rgi7_id) |
rgi6_area_fraction |
number |
Overlap area (overlap_area_km2) divided by the area of the RGI 60 outline (rgi6_id) |
n_rgi7 |
integer |
Total number of RGI 7.0 outlines that overlap the RGI 6.0 outline (rgi6_id) |
n_rgi6 |
integer |
Total number of RGI 6.0 outlines that overlap the RGI 7.0 outline (rgi7_id) |
cluster_id |
integer |
Arbitrary cluster identifier, which groups together all overlapping RGI 6.0 and RGI 7.0 outlines such that each cluster does not overlap any other cluster |
For example, if an RGI 6 outline perfectly matches an RGI 7 outline, the overlap is a 1:1 relation (n_rgi6: 1, n_rgi7: 1) with 100% coverage (rgi7_area_fraction: 1, rgi6_area_fraction: 1). If an RGI 6 outline divided into two outlines (of equal area) in RGI 7, the two overlaps are part of a 1:2 relation (n_rgi6: 1, n_rgi7: 2) with 50% and 100% coverage (rgi6_area_fraction: 0.5, rgi7_area_fraction: 1). Often the relation between RGI7 and RGI6 is more complex, for example when an outline was remapped in RGI 7 and partially overlaps many in RGI 6.