🚀 go-pugleaf

nick@fc.hp.com (Nick Ingegneri) wrote:
>Please forgive me if this posting is off topic for the newsgroups I 
>am posting to, they are the most relevant ones I could find.
>
>I am trying to understand the coordinate values that are printed along
>the sides of some USGS 1:100000 topographical maps that I will be using
>soon.
>
>These maps present coordinates in four different formats, each indicated
>by numbers printed alongside the edges in distinct fonts.  Some of these
>I understand, and some I do not.  Here are some example formats (taken
>from the north-south axis), and my questions/comments.
>
>  Format: { 40o30' }  { 45' } { etc. }
>  Question: No question here, this is the latitude/longitude.
You got this one.

>
>  Format: { 4540000mN } { 453 } { etc. }
>  Question: No question here, this is the UTM coordinate.
Got this one, too.
>
>  Format: { 2 100 000 } { 2 125 } { etc. }
>  Question: These ticks appear to be every 25,000 feet.  What is the
>	    "zero-point" of this coordinate system?
This is one of the state plane coordinates and the zero point depends on 
where you are. You can find out what state plane coordinate sytem you 
are in by looking at the legend in the bottom left corner of your map. 
For example, my map of Richmond, California says that it uses a 10,000 
foot grid based on the California coordinate system, zone 3 (one of 7 
zones California uses). This is a Lambert Conformal Conic projection with 
standard parallels of 37o4' and 38o26', and an origin of 120o30'W, 
36o30'N.
>
>  Format: { T 31 N } { T 32 N } { etc. }
>  Question: I have no idea what these coordinates indicate.  They appear
>	    to be the most useful though, as they line up with the grid
>	    that overlays the entire map.
These are the township numbers. T 31 N is township 31 North. There should 
also be range numbers like R 75 W meaning range 75 West. Look in a 
surveying book or a book on maps to find out what this means.
>
>I would be grateful for a better explanation of the third and fourth formats
>above.
>
>Thanks,
>Nick Ingegneri


Chuck Gantz

In <4ut61e$a3r@fcnews.fc.hp.com>, nick@fc.hp.com (Nick Ingegneri) 
writes: (with deletions)

>I am trying to understand the coordinate values that are printed along
>the sides of some USGS 1:100000 topographical maps that I will be using
>soon.
>>
>  Format: { 2 100 000 } { 2 125 } { etc. }
>  Question: These ticks appear to be every 25,000 feet.  What is the
>	    "zero-point" of this coordinate system?
>
>  Format: { T 31 N } { T 32 N } { etc. }
>  Question: I have no idea what these coordinates indicate.  They appear
>	    to be the most useful though, as they line up with the grid
>	    that overlays the entire map.
>
>I would be grateful for a better explanation of the third and fourth formats
>above.
>

Mr. Nick Ingegneri,

The last two formats are State Plane Coordinate System (SPCS) and the
township and range.

The SPCS is a plane coordinate system, like UTM system. Each state has
its own zone (some more than one).  The coordinate values are based on
"false eastings" and "false northings"  these are arbitrary values
chosen to insure that negative values will not be encountered. 
NGS publications on the subject include the NOAA Manual
NOS NGS 5, "State Plane Coordinate System of 1983" by Jim Stem 
($10.00) or "Fundamentals of the State Plane Coordinate Systems" by
Joseph Dracup for $4.40..To order call the NGS Info Center at
301.713.3242.

The township and range system is another rectangular system
used for the survey of the public land of the US.  You will notice 
township values are indicated as North or South and range values are
indicated as East or West.  A compete description is available in the 
"Manual of Surveying Instructions 1973," from the US Dept of Interior,
Bureau of Land Management.  Its available at many University 
bookstores.

<====================================================>
<===== Donald M. Mulcare        email:dmulcar@ibm.net ========>
<== NGS Advisor to Maryland  410.333.1240 (voice)  ==========>
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