Why it’s not a good idea of mapping the city with GPS?

First thing first it’s a great move by the Greater Chennai Corporation of finally start mapping buildings and collecting the GIS data door-to-door.  In fact, as per the article, the decision of GIS Mapping of the city was taken way back in 2006-07. But finally, the work of mapping started on Wednesday with Ward 57 in Royapuram, Ward 136 in Kodambakkam, and Ward 172 in Adyar.

As per the Chennai Corporation, the vision with GIS mapping is to plan the city better and improve the basic infrastructure such as cleaning garbage, laying roads, providing streetlights and storm water drains etc. Since the GIS mapping vision is not only limited to address and location so, it’s necessary to map those building with accuracy.

The Corporation is using a tablet for collecting require data which means they will use GPS for respective door-to-door location (Lat and Long) mapping . As we all know the average accuracy of GPS in India is 15 meter (Sometimes it’s 30 meters and 10 m  also). I am not gonna talk about the technicality of GPS errors rather the errors is highly affected by following factors.

  1. The quality of phone you are using.
  2. Indoor or outdoor.
  3. AGPS signals such as wifi or mobile network.
  4. Signal Multipath (This also affected by various factors).

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In the above pic, you can see the GPS accuracy in three different environments a. Open Ground b. Indoor, c. Outdoor (House between both side of the road). The building mapping will be based on the third environment. Sometimes you will also see the accuracy of 4 meters but if you will check on the map the error will be close to 15 meters.

The use of tablets mean they will not use wifi and definitely the quality of tablets will be also not very high which leads to reduce the AGPS effect. So, GPS error might increase. Even if we consider the average error of 20-meter in GPS location, the chances of getting the right location (Lat and Long) at every door will be very less. So, after investing much time and money if Corporation is not getting right data that will still not helpful for the city in terms of planning and improving basic infrastructure.

What is the fix?

There are few fix available for improving GPS location

  1. Don’t depend on automatic GPS location. While mapping they can easily see the error, so just adjust the location pointer.
  2. Use DGPS, as they are mapping ward by ward basis in that case DGPS will be very helpful because it can bring down those errors up to 1 meter. But for using DGPS as mapping device they need DGPS receiver and DGPS base station that will slightly costly than tablet but one time investment will give them long term profit.

I believe It’s time to fix the problem from the base especially if cities Corporation is mapping door-to-door. Small attention and few extra tool will solve the problem from the ground which will help everyone.

The purpose of this article is to help them and stop doing the mistakes which we had done in the past. Not only Greater Chennai Corporation if any of the cities corporation is thinking to start mapping, they should start mapping with accuracy.

PS: My favorite quote “Change how people communicate will always change the world”. There are various ways people communicate and I also want to change one of the ways. If you are mad enough to do anything for the Change, it will be my pleasure to get in touch with you.

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