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am working on a project to do country-wide mapping using projected coordinate system such UTM. However, the country (Zambia) is covered by three UTM zones, namely zone 34,35 and 36.I have read literature on possibility of widening UTM zones and the resulting worsening of errors. My concern is on how to modify UTM zones to cover as much as 12 degrees of longitude in one zone. The central meridian will of course be moved to the center.

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    Don't do it! Mercator is suited to narrow areas that are parallel to a particular great circle. Use a projection that suits your area. The internet is retarded on this topic. – mdsumner May 30 '15 at 15:19
  • @mdsumner: There's no need for language like that. – Lightness Races BY-SA 3.0 May 30 '15 at 19:07
  • Related: gis.stackexchange.com/questions/141496 – Chris W May 30 '15 at 20:12
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If your study area covers three UTM zones, just take the middle one to work with.

As you note, the error in the outer parts increases. If this is a major problem for you, think of using a different projection, like Lambert conformal conical or Equal Area. It depends whether you need exact distances, areas or angles. You can minimize distortion on one of these, but not all of them.

UTM is suitable along meridians. For east-west stretching areas, Albers equal-area conic projection is better.

  • Thanks AndreJ, I will consider your suggestion.However, I would still like to explore all the options of modifying the UTM system such as increasing the false easting to 800,000; and reducing the scale factor at the central meridian to 0.926 as suggested by forums.esri.com/Thread.asp?c=93&f=984&t=277480. – Nkole Jun 11 '15 at 0:27

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