USGS quad says "BM", but no datasheet?

[phil_langlois]

Hi,

 

Does anyone know the significance of the "BM"

with a small triangles that occur on USGS

maps? I see one on a quad that apparently has no

NGS datasheet.

 

Phil

[ArtMan]

There are lots of survey marks on the land, only a fraction of which are in the NGS database. Could it be one placed by a state or local agency? Having said that, I would have thought that given the limited number of BM designations on topo maps, that they would likely be ones in the NGS database. But maybe not.

[survey tech]

You are right, Art. Most of the triangle symbols on the topos are non-NGS. Also, some of the NGS markers do not have the triangle symbol.

[+infosponge]

I've often wondered about that too.

Is there a database somewhere of the BM's that show up on the topo maps? They must be cataloged somewhere?! Some of the maps around here have a number next to the triangle and the "BM" label...don't know if that's altitude or some kind of a reference number.

[+Desert_Warrior]

on military maps, benchmarks are indicated by the - BM - symbol. Non-monumented benchmarks are indicated with just the - BM - ,while monumented benchmarks have an - X - with the - BM -. The number following the BMx is the elevation in meters. So for example...

 

A monumented benchmard 1234 meters asl would be:

 

BMx1234

 

and a non-monumented benchmark 963 meters asl would be:

 

BM 963

 

hope it helps.

 

Mike. KD9KC.

El Paso, Texas.

 

Seventeen minutes after her FIRST call for help, police officers arrived to find Ronyale White dead.

 

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