I am usually an ArcGIS desktop user, but keen to start using PostGIS more and I have a really big bit of processing to do. Not sure what functions to use, hopefully someone can help.
I have a polygon dataset (several million features), based on a type of landuse/ landcover classfication (20 categories). I have a number of regions in another dataset.
For each of the regions, I would like to know the area of each landcover classfication.
In ArcGIS (if it was a smaller dataset) I would imagine first adding the region to each of the polygons in the attribute table using a join. Then using "summarize" on the table by region and by landcover classification.
Not sure where to start doing this in PostGIS / SQL.
Wow thanks that has been a huge help.
It has been running a long time (44 hours!) and now I get:
NOTICE: TopologyException: found non-noded intersection between LINESTRING (coords edited) and LINESTRING (coords edited) at (position edited) ERROR: GEOS Intersection() threw an error! ********** Error ********** ERROR: GEOS Intersection() threw an error! SQL state: XX000
I assume this is a problem in the original data - just a case of reviewing the original data or can I first check the topology some how for the whole data? Is there something about accepting certain errors / processing tolerances?