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jncc / bh3-automation

Automation of the Extent of Physical Damage marine biodiversity indicator
MIT License
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Merging interim outputs #4

Open HartmutT opened 5 years ago

HartmutT commented 5 years ago

Annex 3 of the OSPAR guidelines says that the outputs of steps 1, 2, and 3 (sensitivity maps) were combined using the ArcGIS merge tool. The database equivalent of this tool would be a union query. If there were any intersecting or overlapping polygons in the input layers they would persist in the merged map, as a merge does not modify geometries in any way. Is is ok for the merged map to contain intersecting or overlapping polygons?

meganevparry commented 5 years ago

We would wish to select the polygon with the highest sensitivity to show in the combined map where there is an overlap. It is possible that the merging process used previously isn't ideal. If you can think of a better method than using merge that would get rid of overlaps but select the layer with the highest sensitivity to include in the combined map then please go ahead.

LRPettit commented 5 years ago

The merging process should not produce overlaps as the 3 sensitivity maps should cover different areas. If overlapping polygons arise these should be removed as they might affect area calculation (to remove look at the “Removing Overlaps process” section in the StepbyStepMethod).