Location extends to another UTM coordinate zone

Question

I was working on a project that's located in an area in my state. In that area, it cuts between UTM coordinate system zones 31 and 32. What problems will I encounter in representing the map, and how can I attempt to solve the problem?

Answer 1

Short answer

If overlapping is a problem or not depends on two factors:

1. How much the overlap is.
2. What you intend to do (what precision and accuracy you need).

To solve the problem, there also two solutions as well:

1. Split up your map to smaller ones that are completely within the same UTM zone .
2. Look for another projection - one that covers the whole extent of your area of interest.

Longer answer

The problem you'll encounter when extending your map over the extent of your UTM zone is higher distortion. Any projection distorts earth's surface and UTM zones are designed to minimize the distortion. See this statement:

Within these zones the UTM projection has very little distortion. UTM coordinates can be extended into a neighboring zone for seamless operations, but the farther away from the 6 degree zone you move, the greater the distortion.

UTM projection, United States Naval Academy

This site here explains UTM projections very clearly:

GIS Geography: How Universal Transverse Mercator (UTM) Works

[...] scale is constant north-south along the Meridians. But scale varies east-west along parallels. The two small circles are 180 kilometers east and west of the central Meridian at the Equator. The small circles have a scale factor of 1, meaning a distance of 100 meters in the ellipsoid would be the same on the map projection. The centerline of a UTM grid zone has a scale factor of 0.9996. This means that a distance of 100 meters on an ellipsoid would be 99.96 meters on a map.

And:

The UTM projection minimizes distortion within that zone. So this means that when you want to show features in several UTM zone, it starts becoming a poor choice of map projection. Distortion is small near the central meridian, and as you move away it worsens. So this makes it most fitting for narrow regions and not well-suited for world maps.

Universal Transverse Mercator was really meant to map features in one UTM zone at a time [bold in original]. (...) The Universal Transverse Mercator is horrible for small-scale (less-detailed) maps like world atlases and perfect for mapping narrow regions.

See also See also Wikipedia on Universal Transverse Mercator coordinate system: Overlapping grids:

Around the boundaries of large scale maps (1:100,000 or larger) coordinates for both adjoining UTM zones are usually printed within a minimum distance of 40 km on either side of a zone boundary. Ideally, the coordinates of each position should be measured on the grid for the zone in which they are located, but because the scale factor is still relatively small near zone boundaries, it is possible to overlap measurements into an adjoining zone for some distance when necessary.

So the question is rather how much more the distortion gets outside of the extent of the respective UTM zone. Of corse, the more you get away from it, the bigger the distortion gets. So for just tiny overlapping with the neighboring zone, that might not be a problem - but it depends on what you want to achieve.

Edit by user @John Uko:

There is a conceptual error in the contents of the website that is quoted in this answer, which I am correcting :

The distortion is small near the central meridian and it(distortion) actually decreases as we move towards the standard circle and beyond the standard circle, the distortion starts to worsen again.