Rounding numbers in locale friendly way

[Marcus Lundblad <ml update uu se>]

Hi!

In Maps we display population numbers in the place bubbles (typically
for places like towns, cities, states and so on) based on the
"population" tag from the OpenStreetMap database.

In a some cases, where population numbers are more like estimates, this
number can be rounded, say to the nearest 100k.

Currenly we display the number just a normal integer, using the user's
locale.

So, in a cases, where let's say a city is tagged population=1200000

it would be displayed: 1,200,000 in English (and so on, 1 200 000 e.g.
in Swedish).

I have played with the idea to try to "detect" when it's an estimate.

For example, something like:

if population "an even multiple of 1000000":

display _("%s M") where %s is population / 1000000 with one significant
digit.

if population > 1000000 and "an even mulitple of 100000"

display _("%s M") where %s is population / 1000000 with two significant
digits (e.g. one decimal digit).

otherwise just display the number locale-formatted (like is done
today).

Does this make sense? Or would this assumption that millions "M" is an
appropriate concept cause trouble in some languages?

I guess the these would also be using ngettext (with the even muliples
of one million as "n".

//Marcus