[GIS] OSM zoom levels correspond to what level of text labels

labelinglayersmaperitiveopenstreetmap

I'm using Maperitive to render OSM map data of Mexico City as SVG files, destination Illustrator and then print (on paper, in a book).

At different zoom levels, the resulting maps have different levels of text.
At zoom=16 it looks like I get everything down to the last little street name, at 13, far fewer labels.

Since we want to print city maps with just the major categories – like names of suburbs – does anyone know what labels are included with the different zoom levels? If I knew that, I could do the maps without the thousands of street names that would be too tiny to read in print. OSM has something on it:

http://wiki.openstreetmap.org/wiki/Zoom_levels

…but not much.

Once I've worked it out, I want to do other maps of other cities, hoping that the same rules apply in all of them.

Best Answer

What gets rendered at what level (and what size of font etc.) is defined by the rendering rules in Maperitive (BTW these rules are not compatible with Mapnik's). Usually the rule for, say, town name, covers multiple zoom levels in one go. Example: font-size : 5:10;15:20 means the font will have 10 pixels size up (and including) the zoom level 5 and then it gradually increases to 20 (from level 15 and onwards). Whether something is rendered on a particular zoom level is defined by min-zoom and max-zoom properties.

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[GIS] How to “calculate” distance-to-ground of all 18 OSM zoom levels

Some ideas that can help you:

Web tile has a certain resolution (PPI, pixels per inch). You probably want to avoid displaying the tile as a texture that looses a lot of PPI. So a tile that is 256x256 probably wouldn't look too good shown as a 1024x1024 texture.
Each OSM zoom level has its own (approximate) map scale.
Since you say you'll show a flat Earth, you can still calculate the current map scale based on the distance of the observer from the Earth, the latitude the observer is on and the size of the screen.

Once you have the current map scale, you can calculate the zoom level (code taken from my project Maperitive):

public static float MapScaleToOsmZoomLevel(float mapScale, float latitude, float ppi)
{
    const float MetersPerInch = 2.54f / 100;

    const double EarthCircumference = EarthRadius * Math.PI * 2;
    double realLengthInMeters = EarthCircumference * Math.Cos (Deg2Rad (latitude));

    double zoomLevelExp = (realLengthInMeters*ppi) / (256*MetersPerInch*mapScale);

    return (float) Math.Log(zoomLevelExp, 2);
}

Now you have a zoom level as a real value and you can calculate the actual zoom level based on a "quality" setting - for example if you want a higher quality, you can use something like Math.Ceiling(zoom).

[GIS] Generating very simple slippy map tiles

Maperitive only works with small map areas, not the whole planet, since it loads all of the map data into RAM. If you need to cover the whole Earth, you should use Mapnik or TileMill.

Best Answer

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[GIS] How to “calculate” distance-to-ground of all 18 OSM zoom levels

[GIS] Generating very simple slippy map tiles

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