It appears from the QGIS documentation that the Heatmap Plugin can generate a kernel density surface from a point map and make use of the attributes of the original points to influence this surface via the "Use weight from field" option. Does anyone know whether this plugin in QGIS performs the same function as the "Kernel Density" tool in the Spatial Analyst toolbox in ArcGIS? (in the ArcGIS tool, the "population field" can be used as a weighting option--I'm assuming that if this weight is zero, the resulting surface is essentially a "heat map"?).
I was curious so I did a small test to see if the two programs perform the same function. The quick answer is yes and no.
Let's have a look-
Random set of 100 points with a random weight value:
Setup KDE in ArcMap 10.2.1:
Setup KDE in qGIS 2.0.1:
Compare the results. I adjusted the symbology so that the discrete values were equal interval, 6 classes, one for zeros, the rest representing their 20%. Left, ArcGIS, Right, qGIS:
Looks good, right? Well, there's a catch. Remember when I said:
I adjusted the symbology so that the discrete values were equal interval, 6 classes, one for zeros, the rest representing their 20%.
The values in the rasters are completely different. Here's a simple breakdown of those raster values:
- Min: 0
- Max: 1.054002837008738e-006
- Std. Dev: 2.149743379111992e-007
- Min: 0
- Max: 2.6250930968672e-003
- Std. Dev: 5.3712256066864-004
So although they appear the same (yes), the actual output density values do differ (no).
Per the comment by @whuber, the two rasters were divided against each other. I did not take a sample of the two to eliminate edge effect, but I did symbololize the raster so that values 0-2,400; 2,400-2,500; 2,500-2,600; and 2,600+ were drawn.