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The earth is three dimension object while our screen is two-dimension.

So when we use the gis software to display the geographic data, how do they handle the translation between latitude/longitude and screen pixels?

I know the projection which will translate the latitude/longitude to a two-dimension point. But what is the unit of the two-dimension point? Is it the 'pixel`?

Update:

To make this question clearer:

enter image description here

The rectangle is the screen view port(with size 800x600), and I know the center coordinate(65E,26N), then how to get the coordinate of the four corner?

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  • Usually the unit is a meter. This site contains (literally) thousands of examples testifying to this (the link goes to only a few hundred of them). – whuber♦ May 7 '13 at 3:04
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I'm asuming you are talking of how GIS softwares show data with Lat Long on a Flat map, like this: map

Al the GIS Software that I have worked with, inlcuding ArcGIS & Qgis, treat the latlong as linear units, and show the data in pseudo Plate Carree projection.

Now that I think of it, this question seems an exact duplicate of Projecting EPSG:4326 data in 2D map?
Does it answer your question?

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  • Thanks, your answer is helpful. In fact, I want I am building an android application which will render the vector data with styling. Then once the map center is given, and I can get the viewport size, then I have to get the lngat coordinate of the four corners. And Then get the data and change them to screen pixel. That is why I ask this question. Then I wonder if the projection is necessary in my requirement? – giser May 7 '13 at 5:52

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