CHECK YOUR HANDHELD GPS

If you have a handheld GPS receiver and want to check its performance, the county has numerous permanent monuments with known, high precision latitude/longitude values. A map showing the location of those monuments is available here (link to scanned map) or by contacting the County Surveyor. The map has a monument ID number ranging from 101 to 133. The latitude/longitude values for these number points are here.(link to county control.doc).

If you know approximately which point you are near, you can enter the lat/long values into your receiver, then navigate to it. 

Note that the latitude/longitude values shown on this list are in “degrees minutes seconds.decimal seconds” format. You should either reset your receiver to accept this input format or convert these values to whatever format your receiver is set to use. Common formats that I have seen are decimal degrees (where the value you see is like 45.64367°) and “degrees minutes.decimal minutes” like 45°38.6202’.

The following values represent the same latitude position but in different formats:

45.64367°            Degrees
45°38.6202’          Degrees, minutes
45°38’37.21”         Degrees, minutes, seconds

It is very important to understand the format your receiver is using.

All County control monuments are poured in place concrete monuments with brass caps, usually marked with a white vinyl sign posts. Once you find the monument you can compare your observed readings to the published readings. 

Please note that because of the intended use of the county control monuments, they are positioned so there are very few obstructions to the sky. The performance of your handheld unit will be much better at these control monuments than in wooded areas. Keep this in mind if you are trying to use your GPS unit for unintended purposes.