[GIS] How to Determine to world map size in pixel given this data

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How to Determine the world map size in pixels given this data?

Map size of a particular area say, for example:

Makati city, Philippines with bounds:

Top-Right: 121.0281, 14.56497

Bottom-Left: 121.0144, 14.54637

Image size: width="4095px" height="4095px"

Scale: at zoom level 17 | 1:4,000

Now my question is… how can I know the size of the world map in pixels using these available data?

I'm still new to geographic information systems…. so please if possible make it understandable for a novice like me… 🙂

Best Answer

You have tagged your question with OpenStreetMap, so I am assuming you are interested in the data in OSM's zoom levels.

Please have a look at: Zoom Levels

Usually you would not look at the whole world, at the same zoom level, as you would a small city. Your example is at zoom level 17, which has a scale of 1:4000.

You would look at the world either at zoom level 1 or 2.

This is because, at higher zoom levels, a humungous number of tiles would be required. How many you ask? Look at this page: Tile Disk Usage

You will see that at zoom level 17, there are 17,179,869,184 tiles, out of which 429,535,936 have been seen so far. Each is 256 by 256 pixels. And that is a lot of pixels.

Related Solutions

[GIS] Mapserver, TMS, Scales zoom levels and how to deal with all of it

While I can't speak for others, I use Geoserver and had much the same question when I started. Unfortunately, I didn't find a particularly nice feeling solution to it either.

I used the Sld file to put in max and min zoom scales. Same as what you have mentioned as seeming hacky, just choosing 1:40500 for a display betwen level 13 and 14. For all levels I just went off your link to the table and picked something round inbetween.

It would be nicer in this situation to have a MaxLevel and MinLevel that then only renders between those levels, but I guess the scale calculations suffice for most.

[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).

Best Answer

Related Solutions

[GIS] Mapserver, TMS, Scales zoom levels and how to deal with all of it

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

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