I'm trying to determine if an Albers Conic (Alaska Albers) is suitable as a projection for a corridor 800 miles long by 50 miles wide, that goes from the north coast of Alaska to the south coast. This corridor spans 2 state plane zones (west to east).

I need to support survey grade accuracy in my GIS for the corridor, and Albers won't cut it I think. Should I create a new coordinate system composed of a merge of the 2 state plane zones to address the accuracy need?

  • Would it happen to be the Trans Alaskan pipeline? If so, I would wonder if there is a projection specifically for it. – Kirk Kuykendall Aug 8 '13 at 17:03
  • The analysis at gis.stackexchange.com/a/31711/664 shows you will achieve high accuracy with a TM projection. You don't have to use an official UTM zone: you can shift a nearby zone so its central meridian follows the center of your corridor and, for even greater accuracy, you can remove the 0.9996 scale factor. – whuber Aug 8 '13 at 17:07
  • @whuber If it is the Trans-Alaska pipeline, the majority of it falls within UTM 6 and most of that is not along the central meridian. I would suggest that the scale factor shouldn't be 1 at the central meridian whether a UTM or a custom CRS is used. – mkennedy Aug 8 '13 at 19:09
  • @mkennedy, thank you. The scale factor should depend on the extremes of the lateral extent of the area of interest. Although it should be less than 1, in order to balance the (small) distortions created across the area, then if those extremes truly are on the order of 50 miles in either direction, then the scale factor should be greater than the conventional 0.9996. Regardless, if the extremes are less than 200 miles or so (in both directions), one cannot do any worse than UTM (with its scale factor of 0.9996) and might be able to do appreciably better. – whuber Aug 8 '13 at 19:45
  • could a modified transverse Mercator be utilized which is a 3 degree lune with a 0.9999 scale factor or is the width of the study area too large? – user681 Aug 8 '13 at 22:36

I would be tempted to work individually in the two zones if you require that level of accuracy and use the two individual zones for all survey work and technical work. Basically from a survey engineering perspective treat it as two projects then if needed you could do presentation level work in the Albers projection combining the two.

  • the issue is that we need one zone as required by the PODS database, otherwise things get messy in moving up and down the line. Albers is good for presentation, but the real need is a zone that supports surveyor grade data which the GIS is built on. I'm leaning towards a custom State Plane zone with a central meridian north south from Prudhoe through Fairbanks and to the coast. That way we get a good scale factor, and we make the surveyors happy because we're using State Plane. Any thoughts? – user20882 Aug 29 '13 at 2:52

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