The map in which i am building will be used by an Emergency backup 911 system. I am plotting addresses from a csv file and geocoding with google. To do a test I did 100 addresses in a town I am very familiar with (I grew up there). The addresses in which i plotted are way off from where they should be. For instance an address in the 600 block in this town is plotting on the map in the 1000 block. Again I am geocoding it from Google. Information I have looks like this of course with actual real addresses names ect. Address City Zip Name 600 Main Anywhere 99999 Jane Doe

These addresses need to be almost spot on.

  • 3
    Unfortunately, you get what you pay for. You should be researching E911 geocoding provider solutions (which Google is not)
    – Vince
    Commented Jan 29, 2016 at 19:20
  • Do you have Network Analyst? This would be the best option in my opinion for accuracy. You create a route that is calibrated properly, which is where you seem to be getting discrepancies.
    – Petunia311
    Commented Jan 29, 2016 at 19:38
  • Check the google terms of service - there are fairly serious limits on storing geocoded results.
    – BradHards
    Commented Jan 30, 2016 at 4:32

1 Answer 1


There are different geocoders which use different methods and input data.

One approach relies on centroids of either parcel or building data. If the address is 123 Main St, the geocoder identifies the parcel or building with that address and assigns the point location based on the centroid of the polygon This will be inaccurate, for example, when you have a large tract and the building is not located near the center. This is the method that Google uses. In addition, any inaccuracies in the original assessors will show up in the results.

The other method uses street data with block number and related attributes. So, for 123 Main St, it first identifies the 100-block of main street, then determines if odd is on the left or ride side of the street, and then assigns the point location 23% up that block (assuming address on the block range from 100-199). This is the method that ESRI geocoder uses.

I believe that the QGIS plugin can work through either method, though I have only used it with the Google geocoder.

Neither method is perfect and any errors in the input data will show up in the results. For this context, I would suggest that you visually adjust and verify each location using georeferenced imagery.

  • Ive noticed this. When i am at a certain zoom level the addresses are where they should be. When I zoom in the addresses move down the road. How would one "Lock" them in position. Commented Jan 31, 2016 at 6:06

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