Most consumer GPS devices will advertise that they have an accuracy of about 2-3 meters (6-9 feet), but if you’ve ever imported your position and compared it to a known location you’ll realize your data collection isn’t always as accurate as the specs say.

There are a couple of settings on most devices that you can adjust which will allow you to collect more accurate data. You can usually set your device precision by telling it to throw away or ignore information that is not within a user-set range of accuracy. The two settings that you would adjust are the VDOP and HDOP tolerance values.

VDOP: Stands for Vertical Dilution Of Precision. The higher the VDOP value the more diluted or inaccurate your data becomes.

HDOP: Stands for Horizontal Dilution Of Precision. As with VDOP the higher your HDOP value the less accurate your positional information.

Different GPS devices allow you to configure their accuracy in different ways. Some GPS devices will allow you to tell it to ignore high (less accurate) DOP values. By telling your GPS device to ignore the high HDOP and VDOP values you’ll collect more accurate positional data. After adjusting these setting you may notice that your time to first fix (TTFF) takes a bit longer than when you allowed your device to collect data with the higher VDOP and HDOP values – this is normal and it is the price of accuracy. You may also notice some holes in your data collection. If you’ve set your device to collect a point for every second and it can’t get a value that is within your acceptable precision parameters it will just not store a point for that period of time.

You may find that in areas where satellite communication is difficult (mountainous terrain, dense forrest) that you never achieve a positional fix or that you have to wait for one or two minutes before you can achieve one – again this is a normal side effect of asking your device for more precision and you should adjust your device accordingly.

Assess your own situation and the accuracy of data that you would like to collect and adjust your settings accordingly.