Dissolving polygons closers than 50m into a single shape QGIS

Question

I’m new with GIS (coming from a CAD background) and using QGIS 2.0.1. I have a very detailed map of urban fabric in a UK region, to the detail of individual buildings.

I want to simplify that map by uniting regions where buildings are closer than 50m to each other into a single shape. Areas with more disperse urbanization should not be considered - polygons here should be deleted.

The result would be a land use map with polygons delimiting areas of dense building, rather than individual shapes for each unit. I suspect that the “Buffer” tool would do the job, if I choose 50m as buffer distance and combine the buffers into one region.

Before I set out to do it, am I thinking right about this? Or is there other way to do it accurately? Thanks!

Answer 1

You can run a buffer around you buildings with 25m. This way if two buildings areas are at 50 m or less they will now touch.

Then run the dissolve, and all the polygons that touch will merge each other (you will need to create common attribute for this). An alternative is to start edition on the layer, select all features and use the merge selected features in the advanced digitizing toolbar.

In the end, if you want, you can run buffer again, now with the negative value of -25 m. this will contract the polygons to near the initial form and keep the connection between adjacent buildings.

Hope it helps.