How to transform a distance from degrees to metres?

Question

I\'m using OpenLayers with an ordinary mercator map and I\'m trying to sample a bounding box by finding a grid of points in latlong. The bbox is expressed in latlon, e.g.

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Answer 1

The transformation between degrees and metres varies across the Earth's surface.

Assuming a spherical Earth, degrees latitude = distance * 360 / (2*PI * 6400000)

Note that longitude will vary according to the latitude:

Degrees longitude = distance *360 * / (2*PI* cos(latitude) )

The above is for the Earth's surface, and does not use the Mercator projection. If you wish to work with projected linear distance, then you will need to use the Mercator projection.