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Frequently asked questions

What is Resolution?

Resolution is a measure how small a reading is subdivided. If a digital reading has 5 digits, then it has a resolution of one part in 100,000 (00000 to 99999). A reading that has a resolution of 5 digits does not mean that it is precise or accurate to that value. In fact, all it means is that the display you are reading has 5 decimal numbers showing, nothing else. Precision can never be better than resolution but it is usually a lot worse.


What is Precision?

Precision is the measure of the repeatability of your reading. If you take 100 readings of the same measurement, there will be a variation in the readings. The smaller the variation or range of readings, the better the precision. In the case of the Streets & Trips map, the precision is a bit better than 3 decimal places hence the decision to round to 3 decimal places. Does this mean that the readings are accurate to 3 decimal places? Not at all. Accuracy is not related to precision except that precision will put an upper limit on accuracy.


What is Accuracy?

Accuracy is the variation between the measured readings and the true value of the measurement. For example, I can place a location pin on a map and measure the Lat/Long coordinates 10 times. The readings will probably be within a thousandth of a degree (3 decimal point precision). But the accuracy of the reading will be dependant on the interpretation of where the pin should be placed, the accuracy of the reference point to which the reading is compared and the accuracy of the measuring device. I may place the pin in a spot and be able to take readings that are precise to 100 metres but maybe I placed the pin 5km from the true location of the feature or maybe the measuring device is not calibrated and is 10% in error. The accuracy in that case would only be at best +/-5km. Accuracy can be no better than precision but it can often be a lot worse. Unless you understand the underlying errors in the measurements, your reading can often be misleading.


en/np/base/feature_type_catalogue/faq.txt · Last modified: 2010/01/16 13:14 (external edit)