Mac 10.9.5; QGIS 2.8.4-Wien; history and unioned data, in GDA94, zone 55 here.
I have a polygon of fire history with a number of overlapping features. I want to create a new polygon for fire frequency, where each feature has a count of the overlapping features in the history polygon.
The attached data is a small subset of my full data set, so I need a method that will be manageable with a large data set.
I unioned the history polygon to itself to get the individual features that should contain the frequencies. I previously followed Donovan Cameron's method in ArcGIS (http://forums.esri.com/Thread.asp?c=93&f=987&t=282764) with success. However, there is no 'summarize' option in QGIS, so I get stuck at point #6 in that method. I no longer have access to ArcGIS, so I am looking for a QGIS solution.
Here are some other things I've tried:
In another ArcGIS method (gis.stackexchange.com/questions/51929/how-to-count-and-rasterize-polygon-overlaps-in-arcgis-desktop), I get stuck at the 'dissolve' step (step 2) because there is no option to count in the dissolve tool for QGIS.
In the spaghetti and meatball (blogs.esri.com/esri/arcgis/2012/11/13/spaghetti_and_meatballs/) method, I substituted 'Feature to polygon' with union, and used Vector>Geometry tools>Polygon centroids (instead of the suggested Feature to point tool). At the intersect step I get an empty polygon so I tried to use the spatial join then join steps. This produced a range of the counts I was expecting (0-4) but not all of the original unioned polygon features were retained and the spatial configuration of counts were incorrect.
Finally, I've tried raster solutions (e.g. Creating a raster surface of overlaps from vector polygon shapefiles?), but I can't work out how to split my polygon features into separate polygons (multipart to single part returns an indentical polygon).