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Natural Earth polygon corruption changing projections in MAPublisher

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#1
David Medeiros

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I'm re-projecting the 1:110m Land shapefile from Natural Earth in MAPublisher from WGS84 to Van der Grinten. When I do, portions of the land polygon switch sides from East to West, creating bands across the map area. I've seen this with other NE datasets and MAPub transformations as well. Some files and projections work, some don't.

Any idea why this happens and how to avoid or fix it? I feel like I've asked this questions before but can't find my post, I apologize if its been answered in the past.

Edited to add: I checked a few other projections, Winkel Triple, Times, WGS World Mercator... same results. PS, this is the newest NE data set and the most recent MAPub version.

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GIS Reference and Instruction Specialist, Stanford Geospatial Center.

 

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#2
davidwa

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I'm re-projecting the 1:110m Land shapefile from Natural Earth in MAPublisher from WGS84 to Van der Grinten. When I do, portions of the land polygon switch sides from East to West, creating bands across the map area. I've seen this with other NE datasets and MAPub transformations as well. Some files and projections work, some don't.

Any idea why this happens and how to avoid or fix it? I feel like I've asked this questions before but can't find my post, I apologize if its been answered in the past.

Edited to add: I checked a few other projections, Winkel Triple, Times, WGS World Mercator... same results. PS, this is the newest NE data set and the most recent MAPub version.


Hi David

This issue may occur when transforming your data it has extents outside of the envelope of 180W - 180E.
Try checking to see if this is the case with the MAP Location tool, if so, use the MAP Vector crop tool to trim the map extents ever so slightly and attepmt retransforming. Are you centering the transformation on 0,0 or are you setting differing central meridians?

If importing new data you can very if this is the case by using the Advanced importer. First enable the "show extents in Advanced Import table" option with the MAPublisher preferenced Import options then select a dataset for import. You will see the extents denoted by the LLx & URy and should give you a clue if the incoming data should be adjusted. Hope this helps.

#3
Melita Kennedy

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I understand why it's happening (it's fine in ArcGIS). When the coordinates at or near +/-180 are projected, some of them are ending up on the other side of the world. Ex. 180E may end up at -20million rather than +20million. One solution might be to slighly clip left/right before projecting the data (while maintaing the features as polygons). That should remove the problematic coordinates.

I don't know if this is possible in MAPublisher.

Melita

#4
David Medeiros

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Seems to be a MAPub issue. With some playing around and help from Nathaniel at NE I've found that the page size the layer is imported into makes a difference. With a page at a little less than 8x10 you get the polygon inversion, if I use a pager at 24" x 24" there is not problem, even though in both cases the imported art work is sized to exactly fit the art board. clipping away the edges before projecting works as well... but I need all the data since this a world locator.

I'll post to Avenza and see what they say.

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