6 replies to this topic

[ColinS]

This will probably be pretty simple for a lot of people here but I'm having trouble conceptualizing this as I haven't used UTM in arcmap really at all before.

Essentially I'm trying to figure out distortion and north in an area close to the eastern edge of a UTM zone. When I put all the data in in Lambert and set the central meridian to the centre of my area, the townships align directly to the north. In UTM, they are slightly angled.

My question is, is the difference between the norths simply a matter of the distortion between the two projections? Or am I doing something wrong. The coordinate settings in my UTM map have the central meridian a few degrees of longitude off, but that shouldn't even be an option for UTM. Looking at a map of the same area made by an authority more trustworthy than myself, the way I'm doing it is correct for UTM, it's just the differences are blowing my mind a little bit.

Hopefully this makes sense, it's the end of the day and I'm just trying to get my jumbled thoughts out there. And thanks for the help and hopefully the answer isn't so obvious as to be embarrassing.

[David25]

This will probably be pretty simple for a lot of people here but I'm having trouble conceptualizing this as I haven't used UTM in arcmap really at all before.

Essentially I'm trying to figure out distortion and north in an area close to the eastern edge of a UTM zone. When I put all the data in in Lambert and set the central meridian to the centre of my area, the townships align directly to the north. In UTM, they are slightly angled.

My question is, is the difference between the norths simply a matter of the distortion between the two projections? Or am I doing something wrong. The coordinate settings in my UTM map have the central meridian a few degrees of longitude off, but that shouldn't even be an option for UTM. Looking at a map of the same area made by an authority more trustworthy than myself, the way I'm doing it is correct for UTM, it's just the differences are blowing my mind a little bit.

Hopefully this makes sense, it's the end of the day and I'm just trying to get my jumbled thoughts out there. And thanks for the help and hopefully the answer isn't so obvious as to be embarrassing.

Hi,

As long as I understand you correctly I think your answer is that yes, it's just a case of two different projections therefore slight distortion. UTM are more accurate as they are 6degree zones whereas Lambert is nationwide. Also UTM's have their own central meridian and if you're not using the correct one they will look off. At least that's my understanding. I'm not too crash hot on projections but that's my opinion.

[rudy]

UTM Zones being 6 degrees across, I would think that north on the edge of a UTM zone would be 3 degrees off. I can't remember if ArcMap has the option of creating a custom UTM zone with a unique longitude but you might want to try that. Alternatively, add in some grid lines and see if they appear vertical. Somewhere on either the UTM or Lambert projection, north is going to be rotated. Depending on the coverage and scale of your map and the settings of your Lambert projection, the rotated north might not be so noticeable.

[kay]

Which kind of "north" are you talking about (True North, Grid North, or Magnetic North)?

[SouthernCross]

UTM Zones being 6 degrees across, I would think that north on the edge of a UTM zone would be 3 degrees off. I can't remember if ArcMap has the option of creating a custom UTM zone with a unique longitude but you might want to try that. Alternatively, add in some grid lines and see if they appear vertical. Somewhere on either the UTM or Lambert projection, north is going to be rotated. Depending on the coverage and scale of your map and the settings of your Lambert projection, the rotated north might not be so noticeable.

No question that UTM's are more accurate than a Lambert projection. An alternative projection and MUCH more precise projection is to use MTM's. This is almost standard in large urban areas (in Ontario anyways) as they deal with smaller areas and are much more precise.

[Nick H]

No question that UTM's are more accurate than a Lambert projection...

Not always I think, it depends. US State Planes can be Transverse Mercator or Lambert, but in both cases the intention is to keep the greatest scale error to smaller than one part in 10,000.

Regards, N.

[SouthernCross]

No question that UTM's are more accurate than a Lambert projection...

Not always I think, it depends. US State Planes can be Transverse Mercator or Lambert, but in both cases the intention is to keep the greatest scale error to smaller than one part in 10,000.

Regards, N.

This could be the case. I've never dealt with US State Planes. Its possible, however I've never come across this instance. Of course, it depends on the map scale...