[Belgium] whitepaper: Computing a shapefile by Belgian zip codes

[joost schouppe]

Hi Alexandre,

A few thoughts:

* why pay 100 euro's for open data? [1] (note: there's a few errors in this
file, which make it crash on analysis using QGIS. In my own work, I used
ArcGIS FIx Geometry as I don't know the right tools in QGIS)

* Zipcode is a terrible way to handle geographical data, as it often has
completely illogical borders. From a practical point of view you need it of
course, as a lot of data are collected at this info. If at all possible,
the lowest geographical level of a datawarehouse in Belgium should always
be the statistical sector.

* Careful: aggregating statistical sectors into postal codes is not
entirely correct, as statistical sectors do have logical borders. See this
example where buildings are coloured by postal code and overlayed with
statsitical sectors (black lines) [2] . In the website I co-manage [3], we
chose to name these merged statistical sectors "postal codes", even if
that's not strictly true. You can see and download both "our" postal codes
(with imperfect and strange geometry) [4] and our
merged-statsec-to-postalcode [5] from the Antwerp open data portal.

* It's hard to define which sectors to which postal codes. Yes, the letters
often do give an indication, but in this example [6], some postal codes
consist of different letters, and some letters belong to different postal
codes. I think a more correct way would be to do a spatial join of address
points with statistical sectors, then count the most prevalent address
postal code within a certain sector. Join the resulting table to the sector
shapefile (join by attribute niscode), and you can just do a dissolve by
attribute postal code to get the needed dataset.

1:
http://statbel.fgov.be/nl/statistieken/opendata/datasets/tools/big/SH_STAT_SECTORS.jsp
2: http://i.imgur.com/El8b4I4.jpg
3: https://stadincijfers.antwerpen.be/dashboard/
4: http://opendata.antwerpen.be/datasets/postzones
5: http://opendata.antwerpen.be/datasets/stadsdeel
6:
https://stadincijfers.antwerpen.be/databank/?sel_guid=bc4433ff-d734-4a54-b1ba-410e8a8cc975

2016-05-28 13:23 GMT+02:00 Alexandre Detiste <alexandre.detiste at gmail.com>:

> Hi,
>
> I've followed a one-week course & I felt inspired ("once you pop, you
> can't stop")
> so I finally documented these proceedings as I felt
> they might be interresting to other mappers.
>
> As this list is Belgium-specific material,
> this list felt like the best place to share it.
>
> PS: I'm confident one could do the same with Open-Street Map data,
> it's only a matter of how much does cost your developer's time versus
> the one-shot 100€ cost of buying the base data at National Geography
> Institute.
>
>
> Greets,
>
> Alexandre Detiste
>
> --------
>
> http://users.skynet.be/bs366950/whitepaper/
>
> Abstract:
>
> In most datawarehouses, the lowest detail level for geographical analysis
> is the zipcode*sub-city;
> but as in practice the sub-city is generaly encoded in a poor way; only
> the zipcode is usable.
>
> The National Geography Institute provide for 100€ shapefile data at the
> 'statistical sector' level
> that can be processed to get data at zipcode level at
> http://www.ngi.be/FR/FR1-5-2.shtm
>
>
> _______________________________________________
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> Belgium at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/belgium
>



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