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I'm trying to create a heatmap with about 325 points distributed around the city of Houston. (FYI Houston is a major human trafficking in the US: a title shared with LA and Atlanta depending upon seasons and large events).

I'd like to plot the concentrations of these points, but can only get a large circular area around all of them with QGIS' heatmap plugin.

Currently, QGIS only allows whole numbers as its buffer ratio, so I would need to go smaller or possibly correct my CRS. The confirmed human trafficking addresses were geocoded with Google's API, and I have unsuccessfully tried in WGS84, WGS84/Mercator, and Google Mercator.

Is there a better way to do this? Here's a screen cap to illustrate. The results were the same for the aforementioned CRS's.

heatmap fail

PS. I'm also already aware that the current heatmap plugin can only create a raster layer with projected coordinates if the buffer ratio is in map units

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  • Just curious, how did you get this data? Is it collected by police?
    – Fezter
    Commented Mar 6, 2013 at 0:19
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    My guess is that your cell output size is too high. Perhaps, however, you will want to follow an actual tutorial: qgis.spatialthoughts.com/2012/07/…
    – nagytech
    Commented Mar 6, 2013 at 0:22
  • this was compiled by a nonprofit legal counsel for the city. the work was done over the course of last year, cross-referencing locations against multiple sites. i'm fairly confident of the general areas, but just not of the exact locations...hence the heatmap. here's the original @geoist addendums and corrections: the geographic CRS does not work with meters in the current version. projected works just fine. but projected CRS in qgis specify units=m.
    – geraldarthur
    Commented Mar 6, 2013 at 1:21

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If you're curious, it was Tutorial: Making Heatmaps using QGIS and GRASS that helped me learn more. Also, I heard back from the heatmap plugin's creator. Apparently he's been experiencing some bugs as well. If you're using the development version, it should be fixed in a few days.

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  • Can you copy the relevant instructions, in case that link is broken?
    – raphael
    Commented Jan 9, 2015 at 22:07
  • The link was broken and moved as well, the link target is updated. 'Copying' the relevant instructions could be a legal issue, and excerpting the whole article here would be quite time consumin, so ....
    – Jochen Schwarze
    Commented Jul 27, 2016 at 8:59

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