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I am working with the TileMill application to publish layers.

Well, first I have posted directly loading the shp file., But when the charge goes I moved about 200 meters.

Then as I have the option, I imported the layer from postgis and my surprise was that the movement was more than 1000 km.

After choosing SRS: Custom and put the appropriate reference system, the movement returned to be 200 meters.

Does anyone have any idea why this might happen?

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    It would be helpful if you can include your custom CRS in the question, and into which direction the offset goes.
    – AndreJ
    May 27, 2014 at 11:10
  • SRS: "+proj=utm +zone=30 +ellps=intl +units=m +no_defs", displacement is north
    – JFrank
    May 27, 2014 at 12:46

1 Answer 1

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An offset of 200m looks likely to be a false datum shift.

The WGS84 definition for UTM 30N is: +proj=utm +zone=30 +datum=WGS84 +units=m +no_defs

The ED50 definition for UTM 30N looks very similar:

+proj=utm +zone=30 +ellps=intl +towgs84=-87,-98,-121,0,0,0,0 +units=m +no_defs

but has a shift of about 200m to the WGS84 coordinates.

So I suggest to add the +towgs84 parameters to your custom definition.

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