# Dimensional analysis/conversion problem: Map scale to image resolution (dpi)

Given a map scale of 1:17,200 and a raster whose cell size is 6 inches, what resolution (dots per inch) should I choose when exporting the map to an image in order to maintain the raster's native resolution (1 cell = 1 dot). Need a quick refresher on the conversion formulas.

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I found this formula on the ESRI Mapping Center Blog:

1/x = 1 / (pixel ground size [m/pixel] × pixel density [pixels/m]), so that 1 meter on the map represents x meters on the ground

Which, rearranged to solve for pixel density (resolution) is:

pixel density [pixels/m] = x / pixel ground size [m/pixel]

Plugging in my numbers/units this is:

pixel density [pixels/inch] = 17,200 / 6 inches = 2866.67 pixels/inch

That's going to be a big file...

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which begs the question of: is native resolution actually necessary? Do you or your client have a device that can actually print that density? (all the same, thanks for the question and formula!) – matt wilkie Sep 8 '11 at 21:29
That's a good question as well -- I think they want to be able to do their own downsampling for printing hardcopies as needed while still being able to zoom into the native resolution for certain areas. Basically they need their own Image Server but they don't have one :p – blah238 Sep 8 '11 at 21:52