Hot answers tagged buffer
There is a "Distance or Field" parameter in ArcMap's Buffer Tool: http://resources.arcgis.com/en/help/main/10.1/index.html#//000800000019000000 To create the "inside" buffer, just use a negative number of the units.
I guess you have set the CRS for the layer in a false way. If the data was originally in WGS84 degrees, you have to reset the CRS to that, then rightclick on the layer and Save as... If you are in doubt, look at the extent of the layer under Properties, metadata tab. If it is in the range of +-180/90, it is definitely not UTM, but EPSG:4326, WGS84 degrees. ...
You can't in one step. It's a two step procedure. BUT you can simulate the behaviour by creating your buffer as a subquerry. Afterwards you 'select' the buffer area that intersects with your land polygon eg: WITH buffer AS (select st_buffer(point.geom,500000) as geom from data.point_table) SELECT ST_Intersection(buffer.geom,land.geom) from ...
For what it's worth, the ST_Collect() function is much faster then a call to ST_Union(). The speed increase is mainly attributed to the fact that ST_Collect() returns a Geometry Collection object, and doesn't try to dissolve overlapping geometries. You can create a single, OGC-compliant geometry (e.g. a POLYGON or MULTIPOLYGON) by wrapping ST_Collect() in ...
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