[QGIS-ZA-user] aggregate crime attribute data from SAPS Station boundaries to Wards

[Gerbrand Mans]

Hi Brian

You need a proxy variable to predict what the proportional contribution from each ward would have been to get to the total murder rate for the station area.

One way will be to use socio-econ profiling, but you do run into certain biases which may become problematic when you need to explain your method to your users of the output. Else it is just going to be a straight proportional redistribution to wards based on total population per ward if you assume the probability is the same across the police station area.

Best rgds
Gerbrand Mans
>>> Brian O'Leary via qgis-za-user <qgis-za-user at lists.osgeo.org> 03/10/2018 12:26 >>>
Hi Gavin,

attached are the Durban police station boundaries with murder attributes for the last 10 years. Also attached are the Ward boundaries. Any advise on how to produce an output table with murder by ward would be much appreciated.

Thanks
Brian

On Wed, Oct 3, 2018 at 8:53 AM Gavin Fleming via qgis-za-user <qgis-za-user at lists.osgeo.org> wrote:


Hi Brian

Please share a few overlapping station and ward features with the list.

thanks

Gavin



On 02 Oct 2018, at 10:57, Brian O'Leary via qgis-za-user <qgis-za-user at lists.osgeo.org> wrote:

Dear QGis SA,

I would like to know if there is a QGis tool that can assist with the following task. I want to transfer crime attribute data from SAPS Station boundaries to Ward boundaries, assuming that crime is evenly distributed within the SAPS Station boundary.

Previously I have done this task in Arc View using a script called DataPart.avx which was written by Jianwei Dou in 2002. The below simplified sketch illustrates what I am trying to do in Qgis. The SAPS Station shape has the data attributes and the Ward shape is the overlay or boundary shape. The output that I need is an attribute table that has calculated the % intersection of the SAPS Station by the ward boundaries and aggregated the crime attributes to a Ward table based on the % intersection. In the below sketch the ward boundaries intersect the SAPS Station boundary by 50% in both cases. As there were 100 crimes in the SAPS Station boundary the output table lists Wards 1 and 2 with 50 crimes in each.

<image.png>
Any advise most welcome.

Regards
Brian O'Leary



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