The Newer USGS Topo Maps and UTM questions

[Eagle92]

Ok, I'm in the process of getting some topo maps from training, and found free, I don't know their exact name but for argument sake call them, Topo maps from the US Geological Survey on the internet.

 

In some aspects I like them better than the old school topo maps, b/c they use satelite images with the topo info on top. So you see the actual quad instead of a drawing of it.

 

But one thing I noticed is that the grids on it were crooked. Then I noticed that the grid is a UTM grid, not the old Lat and Long. grid. Doing research, I can see how UTM makes it a bit easier to find your exact location since it is based on the metric system. I like that.

 

But my question is this, since the grid is crooked, which whould be used to represent true north: top of the page,or the UTM grid lines?

 

Also in regards to marking the map for declination, should I create Lat and Long lines, then do the Declination ones, or should I use the UTM grid lines and use declination off of them.

 

This old fogey is trying to learn a new trick, so please bear with me.

 

Thanks in advance.

[Eagle92]

Just ignore the entire thread. I found the info I needed.

[eisely]

Eagle92,

 

Not to worry. All can be explained. Unfortunately the space limitations here will not allow a full explanation.

 

As far as I know, all maps published by USGS are published oriented on true North. Hence the need for declination when working with a compass.

 

The UTM system establishes "grid North" within its grid zone. The globe is divided into 60 grid zones at the equator. Within each grid zone, grid North never changes. One will occasionally see civilian maps with declination diagrams showing grid North in addition to true North and magnetic North.

 

What you think may be crooked lines are are simply grid north lines that are diverging from true North, the closer you get to the poles and the further East or West you get from the center of grid zone.

 

Latitude and longitude are sometimes referred to as "geographic coordinates" as distinct from UTM coordinates. While any point on the surface of the earth can be accurately described using the geographic coordinates, the longitude lines are not parallel lines and converge on the poles. Hence it is difficult to use the older geograpic coordinate system for certain applications; for example, gunnery problems in the military. The UTM system provides a set of Cartesian coordinates that can be used to describe and locate any point within a grid zone. The North-South grid lines in the UTM system are parallel and do not converge.

 

In our council there are three districts that provide training on a collaborative basis and we maintain a web site for training materials. Go to the link provided below. It will take you to a pdf file that I created for map and compass skills. Go to page 9 of this file for a more detailed explanation of these coordinate systems.

 

http://www.3districttraining.org/OLS/MapAndCompass/Map_Compass_materia_Oct18_2011.pdf