[OSM-talk] Map of Population Density vs. OpenStreetMap density

Darafei "Komяpa" Praliaskouski me at komzpa.net
Sun Jul 7 10:33:21 UTC 2019

On Fri, Jul 5, 2019 at 3:42 PM Christoph Hormann <osm at imagico.de> wrote:

> On Friday 05 July 2019, Darafei "Komяpa" Praliaskouski wrote:
> >
> > http://disaster.ninja/live/
> > <http://disaster.ninja/live/#overlays=alert-shape-GDACS_EQ_1183112_12
> >65046,bivariate_class;id=GDACS_EQ_1183112_1265046;layer=default-style;
> >position=-13.88712117940031,30.076044779387132;zoom=2.4760319802318693
> >>
> >
> > What do you think?
> Are your densities in people/object per ground square kilometers or per
> mercator square kilometers? (just to be sure - this is the number one
> mistake of any kind of density analysis in the OSM context)

These are ellipsoid based square kilometers. I also dislike when
visualizations fade out to the poles :)

> One warning:  All global population data sets that exist are rough
> estimates with usually significant systematic biases and errors.  For
> example in Switzerland the data set you used sees high population
> density in mountain areas with no basis in reality.

We're using GHS population grid in Switzerland.
Methodologically, they use radar data to find "houses". It means on their
dataset people also live along roads with asphalt, and - may happen - bare
rocks are also populated. You can drop them a line on
jrc-ghsl-data at ec.europa.eu to say thanks.

Is there a better resolution population dataset for Switzerland?

To fix it we can get "unpopulated areas" polygons from OSM. I see that
forest, fields, water, quarry are likely candidates to be used to mark
population as zero, if no buildings are present in OSM. What tagging would
be used for unpopulated mountain?

> And i am not a fan of deliberately pixelated visualizations where the
> data is shown in a pixel grid at a coarser resolution than what the
> display offers.

Can you point to a better visualization which we can learn from?
Map is supposed to be used on settlement level, where our grid is "4 pixels
per screen" - to highlight a settlement without trying to predict its

> Apart from that this is an interesting analysis.  It would be kind of
> nice to also do it separately for density of features that actually
> correlate with population density in reality (buildings, roads,
> addresses, shops etc.) and physical geography, which can be mapped just
> as densely in areas with no population as in densely populated areas.

We've built such map initially, and it's not significantly different from
this one in disaster mapping perspective. People don't map physical
geography far from their home much in OSM, and large unmapped regions don't
become more mapped if we lower feature counts in more mapped regions.
Note that any large multipolygon is counted as just 1 feature here.

Darafei Praliaskouski
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