Take the 2-minute tour ×
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

I have a shapefile with multipart geometry (multipolygons), namely communities (blue on the picture below). There are also lakes (white), but for these I don't have a geometry, they're just "empty".

I want to conduct a point-in-polygon analysis with another point dataset. Each point should be assigned to a community or be deleted when it falls outside a community (e.g. in a lake). The problem is that there are many points for lake-bordering communities that are very close to the shore. Because of the strong generalization, these points get accidentally deleted even though they would actually belong to a community.

enter image description here

The only thing I can think about is somehow to extend the shore line of lake-bordering communities by about 100m, but I'm wondering whether there is some way of doing this automatically in QGIS. I have no clue though I would approach this problem.

share|improve this question

1 Answer 1

up vote 2 down vote accepted

The problem with buffering is that the buffers will overlap, and you need to set an exact value for the buffer distance which may be difficult to get right.

Instead, measure the distance from each point to the closest polygon. Then decide on a threshold for inclusion in a community, or interactively choose for outliers.

Possible methods are available by Calculating the minimum distance between points and polygons in QGIS.

share|improve this answer
    
Very good idea, thanks! –  wnstnsmth Jul 17 '13 at 14:06

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.