QGIS giving multiple centroids per polygon?

Question

I have a shapefile for the boundaries of European NUTS regions, and I would like to compute the centroid for each of those regions. When I do this in QGIS (2.6.1 on OSX, using polygon centroids from the fTools menu), I get multiple centroids per region. Sometimes the centroids are nearly overlapping, sometimes they are further apart. How can this be? Am I doing something wrong? To be complete: I am using the NUTS_BN_60M_2006.shp data, available from Eurostat

I've added a screenshot; this part is particularly bad, but other regions have the issue as well.

Answer 1

The reason are multiple overlaps. If you select ones with STAT_LEVL_=0, they are countries, e.g. NUTS_ID=DE is Germany.

They are 34 largest polygons containing smaller levels, i.e. STAT_LEVL_= 1 (115), 2 (317) and 3 (1461).

Select level you'd like to work with, they are overlaps free. However some of them are multipart features, e.g. FR(ance), because it contains islands, thus it is good idea to explode them (see Chris Hogan answer)

Answer 2

If the responses by @joseph and @Simbamangu does not point you in the right direction:

Are your polygon multi-part or single-part features?

If you have one NUTS region with multiple separate polygons, QGIS will create one centroid for each. If your data include multi-part polygons you will likely get a single centroid with the centroid in the center of the bounding box for all of the polygons in the single multi-part feature.

QGIS has a tool 'single parts to multipart'