subject: Accuracy of Making Land Mesurements and Farm Maps Using Google Map Applications [print this page] Accuracy of Making Land Mesurements and Farm Maps Using Google Map Applications
Accuracy of Farm Mapping Applications using Google Maps
Alongside being a great way to locate and navigate to places google maps also provides a number of area and length measurement functions. These allow for the development of web applications that allow the user to measure distances and land features online. Such applications replace the need for specialised and expensive map making services as well as allowing the user easily and quickly create maps and measurements as and when they are needed.
As we know google maps relies on satellite imagery and so its accuracy is dependent on its resolution. Resolution is essentially the size of the smallest object that can be detected and meaningfully identified in the image. Thus, an image where we can read a number plate of a vehicle is of a higher resolution than one in which we can only see the outline of the vehicle itself. And so it follows that the better the resolution the more possible better and more accurate measurements can be made on it. Generally speaking urban areas have higher resolution or accuracy than rural or remote areas as do European countries over the US. Resolution can vary between a lousy 50 meters at the low end up to an impressive 0.15 meters at the high end. Increasingly this accuracy is improving.
Of course the test of a pudding is in the eating and so lets measure some objects of a known size and length. Specifically lets use the farm-file application to measure the Pentagon USA, the Colosseum Italy and Manchester United's football pitch in the UK. These represent, respectively, an irregular, elliptical and regular shape. Additionally they represent typical feature sizes for large, medium and small farms. A graphical representation of these results can be seen at farm-file.com. But a summary is given here:
Pentagon (Central Plaza) Actual Building Area = 116,000 square meters Measured = 116,100 square meters Accuracy = 99.91%.
Colosseum, Actual Building Area = 21,000 square meters Measured = 21,167 square meters Accuracy = 99.21%.
Manchester United Football Pitch Area = 7,140 square meters Measured = 7,100 square meters Accuracy = 99.44%.
We can therefore see that this particular application is extremely accurate in measuring land areas. In fact accuracies up to 99% can be expected on land areas from a football pitch upwards. This coupled with the obvious convenience of making virtual, accurate measurements of large objects against physically measuring them commends these applications to land managers everywhere.
