Student struggling with projections.

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03-13-2012 10:23 AM
GilesKing
New Contributor
Hi all,

I have been using ArcGIS for less than a year now and am stuck with my dissertation project in my final year of University. I am doing a hypothetical (not so much anymore) situation of Libya splitting into its old regions of Cyrenaica and Tripolitania (east-west) and delimitating their territorial waters.

Basically I have the following geotiff.............................................. http://www.ngdc.noaa.gov/mgg/ibcm/ibcmbath.html
And I wish to use the following maritime boundaries.......................... http://www.vliz.be/vmdcdata/marbound/index.php

Now both will reference with each other in WGS84 although for the purpose of my dissertation, I have to convert these into a transverse Mercator, preferably UTM. The image says it is referenced to 38deg. N which sounds like a UTM but nothing else will even come close to referencing to it, they're all distorted and out of shape when changing the coordinate reference system through Arc catalog. The university does not have access to some of the tools to use GML coordinates that the vliz website also offers.

I am really stuck with this and any help would be greatly appreciated

Thanks, Giles.
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HardolphWasteneys
Occasional Contributor III
Giles,

The main problem with using a UTM projected output for your project is that you have to cross 2 UTM zones to cover Libya and so you will have a lot of angular distortion.  You will also have to choose between Zone 34N and 35N. [ATTACH=CONFIG]12839[/ATTACH]

The attached image shows the low res version of the files you mentioned in WGS-84-UTM Zone 34N projection.   I just georeferenced the smaller raster from the NOAA site in WGS-84 using lat-long coordinates and links to the shapefile rather than downloading the 158 Mb Geotiff.   If you looked at the whole bathymetric map across the Mediterranean in that same Zone 34N  UTM projection it forms a broad curve centered about the UTM zone of choice, which is not really appropriate. 

So it is probably better to use something like Africa Albers Equal Area Conic projection for your final map.  This is shown in the next image with the same files.  It preserves areas better; i.e. is relatively equal in scale N-S and E-W.[ATTACH=CONFIG]12842[/ATTACH]

You can also easily use some of the on-line imagery and boundary data from the "Add_Data_From_the_Resource_Center..." under the File menu, which I included to show the present/previous political boundaries.


Hardolph
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