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Alignment, after projection

April 09 2010 | 0 comments
Categories: Map Data

When I display a 10-meter NED (downloaded from Seamless Server) in its native NAD83 GCS, it is aligned vertically & horizontally. However, when I project it to, e.g., UTM 11 North, the resulting image 'tilts' to the right. Can you suggest a way to 're-align' the map image?

Thank you!

Mapping Center Answer:

It should tilt to the right as that is the alignment of north in the new coordinate system.  However, you can also modify the central meridian of the new coordinate system so that it is in the center of your DEM and that should "straighten" it up.  First, right click the name of the data frame in the Table of Contents.  Then click the General tab and set the Display Units to Decimal Degrees.  In data view, place your cursor over the east-west center of the extent of your DEM and look at the lower left corner of the ArcMap window to see the longitude at that location. Note that number down as you will use it to modify the central meridian.

Now right click the data frame again and click the Coordinate System tab. Here click the Modify button at the right and input a number that you round to something sensible for the Central Meridian.  Click OK and you should see your data "straighten up".

This is discussed in detail along with other information that relates to this very topic (like also modifying the standard parallels and exporting the data using the data frame's projection) in the One Minute Cartographer presentation that you can download from our Other Resources - Presentations page (we gave this presentation at the 2009 ESRI User Conference.) If you download and open the PDF of the presentation, you will see that the bottom notes include complete instructions and explanations.

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