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<p>Hello Brian,</p>
<p>What Gerbrand says is absolutely correct, but taking your
assumption that crimes occur the same over the total area of the
ward you would need to work out the crimes/km2 or so first. From
there on it is a pretty straight forward exercise with QGIS. That
involves a few steps however:</p>
<ol>
<li>Add the two layers to your map</li>
<li>Set your project projection to Zangi:Zangi:CPNO31 (and area
units to km2, if that's what you want)</li>
<li>Then use the vector function "Union" on the two layers to
create a new polygon layer which essentially is a combination of
attributes on the two</li>
<li>The you will notice that there are a few polygons that are not
"unioned" as they don't overlap (e.g. policing areas outside
your wards): make the new layer editable and delete those. You
should then have 367 polygons with "unioned" attributes (I
noticed that there are a few small ones inside the
wards/policing areas due to not-adjoining polygons..these should
be sorted out first!).<br>
</li>
<li>Then use the field calculator to create new columns for each
year category by taking the "number of murders" / $area to get
the murders per km2 (scary!!)</li>
<li>Then use the Vector Analysis Tool "Statistics by categories"
(you are on QGIS 3?) to do a statistic on each of the new year
columns using the ward ID or number (or both) as Field with
categories where you would get min, max, mean, etc. but the mean
is a pretty good assumption in murders/km2 as it is a ratio.<br>
</li>
<li>Then you join the Union table with your results for each year
and save the layer (using selections) to a new table with only
the columns you want. You could convert the murders/km2 back to
the total murders in the area (inverse) beforehand.<br>
</li>
<li>"Bob's your Uncle"</li>
</ol>
<p>Hope his helps!</p>
<p>Immo<br>
</p>
<br>
<div class="moz-cite-prefix">On 03/10/2018 14:20, Gerbrand Mans via
qgis-za-user wrote:<br>
</div>
<blockquote type="cite"
cite="mid:5BB4B408020000F6002DDB65@pta-imo.csir.co.za">
<meta name="Generator" content="Novell Groupwise Client (Version
14.2.2 Build: 126868)">
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charset=windows-1252">
<div class="GroupWiseMessageBody"
id="GroupWiseSection_1538568229000_GMans@csir.co.za_265DD78018ED000096CE00142223C9D6_">
<div>Hi Brian</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>Best rgds</div>
<div>Gerbrand Mans<br>
</div>
<div class="GroupWiseMessageBody"
id="GroupWiseSection_1538568229000_GMans@csir.co.za_265DD78018ED000096CE00142223C9D6_"><span
class="GroupwiseReplyHeader">>>> Brian O'Leary via
qgis-za-user <a class="moz-txt-link-rfc2396E" href="mailto:qgis-za-user@lists.osgeo.org"><qgis-za-user@lists.osgeo.org></a> 03/10/2018
12:26 >>><br>
</span>
<div>
<div dir="ltr">Hi Gavin,
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>Thanks</div>
<div>Brian</div>
</div>
<div><br>
</div>
<div class="gmail_quote">
<div dir="ltr">On Wed, Oct 3, 2018 at 8:53 AM Gavin
Fleming via qgis-za-user <<a
href="mailto:qgis-za-user@lists.osgeo.org"
moz-do-not-send="true">qgis-za-user@lists.osgeo.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin: 0px 0px 0px
0.8ex; padding-left: 1ex; border-left-color: rgb(204,
204, 204); border-left-width: 1px; border-left-style:
solid;">
<div style="-ms-word-wrap: break-word;">
<div>
<div class="m_7977297716352025683moz-signature">
<div style="text-align: center;">
<div>Hi Brian</div>
<div><br>
</div>
<div>Please share a few overlapping station and
ward features with the list.</div>
<div><br>
</div>
<div>thanks</div>
<div><br>
</div>
<div>Gavin</div>
</div>
</div>
</div>
<div><br>
<blockquote type="cite">
<div>On 02 Oct 2018, at 10:57, Brian O'Leary via
qgis-za-user <<a
href="mailto:qgis-za-user@lists.osgeo.org"
target="_blank" moz-do-not-send="true">qgis-za-user@lists.osgeo.org</a>>
wrote:</div>
<br>
<div>
<div dir="ltr">
<div dir="ltr">Dear QGis SA,
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>
<div><span
id="m_7977297716352025683cid:ii_jmrgqim70"><image.png></span><br>
</div>
</div>
<div>Any advise most welcome.</div>
<div><br>
</div>
<div>Regards</div>
<div>Brian O'Leary</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
</div>
</div>
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