[OSM-talk] Wrong scale in slippy map

[Eugene Alvin Villar]

There's a trac ticket submitted two weeks ago for this:
http://trac.openstreetmap.org/ticket/1704

I imagine that the solution would be similar to how Google does their map
scale indicator in Google Maps.

The map scale should be correct for the latitude at the center of the map
view. The map scale is, of course not as useful in lower zoom levels.


On Thu, Apr 23, 2009 at 7:51 AM, Lars Aronsson <lars at aronsson.se> wrote:

>
> Looking at the area where I live,
> http://www.openstreetmap.org/?lat=58.407&lon=15.600&zoom=18&layers=B000FTF
>
> these buildings are 11 metres wide and not 22 metres as the scale
> indicates. The difference is explained by the latitude 58.4
> degrees and cosine(60°) = 0.5.
>
> Maybe one year back, I reported exactly this bug in JOSM and it
> was fixed.  Now I find it in the slippy map.  How long has it been
> there?  Is it an OpenStreetMap bug or a OpenLayers bug?
>
> The metre was once defined as one ten-millionth of the distance
> from the equator to the north pole.  Each latitude degree (of
> which there are 90) is thus 111 km long, everywhere.  At the
> equator, each longitude degree is also 111 km, but at the latitude
> of 60° (Oslo-Stockholm-Helsinki-St. Petersburg), each longitude
> degree is only 56 km.  At each zoom level of the slippy map, the
> longitudes (meridians) run vertical at a constant pixel width,
> meaning that the scale (metres on ground to pixels on screen)
> changes as you pan north or south.  The scale is different at the
> top and bottom of the screen, very much so at the low zoom
> numbers, but insignificantly at the higher (deeper) zoom levels.
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/talk/attachments/20090423/a1e6c93e/attachment.html>