Subscribe to MeaseyLab Blog by Email

Coordinate precision errors

07 August 2015

What does it mean when we give lots of decimals behind the degrees?

Many of us have GPS devices which give us locations in decimal degrees, but what do all those decimals really signify and can we rely on them? In the image below, Alex Rebelo has set out a series of increasingly accurate data points (using Kenilworth Race Track in Cape Town as his example). 

You can clearly see here the difference between giving two decimal places and three decimal places is about 1km!

Should you ever give 5 decimal places? Unless you are using a survey GPS, the answer is no. 

Most handheld GPS units can get an accuracy of around 6-8m, so giving 4 decimal places is realistic. For most of our purposes (usually mapping frogs), this accuracy level is fine.


To use the DISQUS service as your comment system in this blog, you should have a DISQUS account and register your website.

  1. Log into your DISQUS account
  2. Copy or make a note of the site shortname shown in the "Settings" under "Site Identity".
  3. Now log into the C1 Console of your website and edit the page with the "Composite.Community.Blog.BlogRenderer" function.
  4. In the function properties of "Composite.Community.Blog.BlogRenderer", select the "Comments Service Keys" parameter, switch to "Constant" and enter the site shortname.
  5. Click "OK" to save the changes, then save and publish the page.
Creative Commons Licence
The MeaseyLab Blog is licensed under a Creative Commons Attribution 3.0 Unported License.