[OSGeo Africa] Comparing census and elections datasets

[Gavin Fleming]

Hi Adi

The CSIR produced (still  produces?) a product called GAP, which 
aggregates or disaggregates many datasets to a common 'mesozone' layer 
where each polygon is roughly 50 sq.km and has boundaries based on those 
of other administrative layers or natural features. A published 
methodology is used to perform the aggregation / disaggregation. There 
are all sorts of statistical pitfalls in aggregating and disaggregating 
data into different areas and this methodology tries to address them. It 
isn't a simple task to do accurately.

http://www.gap.csir.co.za/

I'd suggest you try and obtain the GAP material and in particular the 
methodology and mesozone dataset. Doing this would result in more 
'interoperable' results since the mesozone units become the ideal unit 
of comparison.

Gavin

On 13/04/2014 22:44, Adi Eyal wrote:
> Thanks Hanlie and Charles
>
> Sounds like that's the only way to go. I was hoping that secretly,
> StatsSA was remapping census data to various shapefiles. Charles,
> happy to take a crack at it with you to try to develop a script that
> will allow this remapping across different boundaries.
>
> Adi
>
> On 9 April 2014 10:14, Charles Rethman <rethman at me.com> wrote:
>> Dear Adi and everybody,
>>
>> I've been thinking about this. I think whatever happens you'll need to do
>> some cookie-cutting.
>>
>> The best solution I think would be to make your algorithm in PostGIS and map
>> it on QGIS.
>>
>> If you like, we could meet up and discuss the details further--and post our
>> trials or results back to this forum? Where--Codebridge? contact me on
>> rethman at me.com.
>>
>> Charles Rethman
>> Wahenga Ltd.
>> Director, Cape Town Office
>>
>> Cell: +27 71 6735502
>> Tel: +27 21 6861510
>> Skype: cwrethman
>> PO Box 23507, Claremont, 7735, South Africa
>> 19 Sans Souci Road, Newlands, 7700, Cape Town
>>
>>
>> On 8 Apr 2014, at 7:12 AM, Adi Eyal <adi at code4sa.org> wrote:
>>
>> Hi All
>>
>> I would like map demographic data from the 2011 census on top of
>> elections results from 2009. There seem to be two problems with doing
>> this.
>>
>> 1. Old wards have disappeared and new ones have been created by MDB.
>> 2. In some cases the same ward id has been re-used for completely
>> different polygons.
>>
>> In short, the obvious approach of joining two datasets won't work. It
>> is possible (but difficult) to calculate approximations by overlapping
>> shapes from the two maps and using some sort of algorithm (possibly
>> assuming uniform distribution of data points) to slice up one shape
>> and fit it into another.
>>
>> I don't want to go down that route.
>>
>> Is there another to go about this?
>>
>> Thanks
>> Adi
>>
>> --
>> Adi Eyal
>> Director
>> Code for South Africa
>> Promoting informed decision-making
>>
>> phone: +27 78 014 2469
>> skype: adieyalcas
>> linkedin: http://za.linkedin.com/pub/dir/Adi/Eyal
>> web: http://www.code4sa.org
>> twitter: @soapsudtycoon
>>
>> For more information on how to participate in the open data community
>> in South Africa, go to: http://www.code4sa.org/#community
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>


-- 
regards

Gavin

Gavin Fleming
http://afrispatial.co.za
t: 0218630660
c: 0845965680
f: 0866164820