fix: missing minZoom on towns

[jgillich]

On towns with a population, it would fall back to the default places zoom of 7. This sets a mininum of 8, similar to other place types.

Also sets fallback population of cities to 50k instead of 5k

ref #506

Before & after:

[jgillich]

Any feedback from maintainers? @bdon @wipfli Thank you :wink:

[wipfli]

Hi @jgillich. Thanks for bringing up this topic. I am not sure how to best go about place ranking. At the moment we use the classification from OSM and the total population I think. And there is a list for minzooms somewhere of a few places (maybe 10k or so). Going forward I think an interesting option could also be to work with QRank as an additional signal for the importance of a place. A combination of OSM classification, population, QRank, and an exceptions list could be a good strategy maybe.