Undersized polygons - remove?

posted 28 Nov 2011, 17:20 by David Pairman   [ updated 1 Jul 2012, 21:58 by David Pairman ]
There are many polygons smaller than the LCDB  minimum map unit size of 1 hectare. Should we remove these, and if so, at what threshold?  

The LCDB claims a minimum map unit size of 1 ha. We’ve removed some of the really small polygons (< 0.05 ha) but among the 400,000 polygons in the database there still remain 67,000 polygons (17%) smaller than a hectare, 16,000 polygons (4%) smaller than half a hectare and 1,200 smaller than 0.2 hectares. From our observation, the smaller they are the less likely these polygons are to resolve any real difference in land cover so we’re contemplating a further elimination step before release in July. What do you think?

Collaborating agencies: Please leave your views as comments below, along with your name/organisation.

These cyan coloured polygons, near Dargaville, are <0.5 ha! (click on image to expand)


At the April 2012 Technical Advisory Group meeting it was resolved to automatically eliminate polygons smaller than 1000 square metres (0.1 hectares). While the minimum mapping unit is nominally 1 hectare, it was recognized that some smaller features have been deliberately mapped and we didn't want to loose these.