topic Re: Different lat and long for same address in Data Management Questions

Different lat and long for same address

St_A — Wed, 29 Aug 2018 15:44:02 GMT

I Geocoded a list of address (Mostly intersections) for bus routing and the same address was geocoded by a different company. The lat and long values that I get is different from the one from the company. I calculated the difference in excel as shown below. Some seem too big. My question is how much is too big? (Calculation in metres). Looking at the table and map it seems not too far off but when I measure the distances in a straight line it seems much as shown in the table. I used projected coordinate system. I am trying to decide which of the coordinates(Lat/long) is the more precise and accurate so the bus will not miss a student. Is it okay to get varying lat and long for same address? Please can anyone help? Any help with geocoding intersections will be appreciated. I checked the match with no house number to Yes.

Thank you

Re: Different lat and long for same address

JoeBorgione — Wed, 29 Aug 2018 15:55:41 GMT

You mention that you geocoded a list of addresses. What data did you match against? Is it your own? Is it from a reputable source?

If you add the company address points to the street data you'll use to create your network dataset, what sort of precision do they have compared to your points? That is, which points fall in the intersections as they should?

Re: Different lat and long for same address

St_A — Wed, 29 Aug 2018 15:58:45 GMT

I used the City's street network data to create my reference data before geocoding. I am not sure which data the company used. Could this be a factor in the difference. Is the difference too much to neglect?

Re: Different lat and long for same address

St_A — Wed, 29 Aug 2018 16:01:12 GMT

Also the points are close most of the time just not on top of each other until you zoom out. I am just curious why they don't match very closely.Thanks for replying me very fast. I appreciate

Re: Different lat and long for same address

DanPatterson_Retired — Wed, 29 Aug 2018 16:19:12 GMT

What is the difference between expectation and observation? A meter?, a couple? 10, 20, 50?.

big differences could be due to errors in coordinate systems and/or projections. smaller differences could be attributed to precision and accuracy

Re: Different lat and long for same address

St_A — Wed, 29 Aug 2018 16:27:02 GMT

MeterDifference	ArcGisCoords_For_Google	GeoFrom_trapeze
552.7224544	53.4608055278, -113.37762709	53.460658, -113.385945
550.109075	53.4605877774, -113.385961346	53.460739, -113.377683
300.4362706	53.4285407575, -113.53653838	53.430043, -113.532783
299.5025307	53.626076525, -113.533326156	53.624516, -113.537014

Thanks Dan for your reply

I sorted the coordinates and above is the ones with the most difference. The difference is in metres. I am trying to figure out if I should exclude/ re-geocode those with the big difference like 552 metres. Thank you

Re: Different lat and long for same address

DanPatterson_Retired — Wed, 29 Aug 2018 17:09:59 GMT

if the rest are much smaller, then one or the other is in error... buildings don't move unless they are on wheels. I would do the google thing and check the points to see the the long/lats look plausible. Perhaps one of the two points is in a field or a lake or something obvious, indicating an error in geocoding or the collected data

Re: Different lat and long for same address

St_A — Wed, 29 Aug 2018 17:16:46 GMT

Thanks Dan. I think the difference maybe due to different reference data used. On checking through I realized the high numbers are not 100 % match hence the big difference. My question is does different reference data produce different lat and long for intersections and buildings, in the case where it goes with one side of the intersection versus the other side(L/R) OR a pin on the building roof versus parking lot or back door.

Re: Different lat and long for same address

JoeBorgione — Wed, 29 Aug 2018 17:48:26 GMT

Varying results of geocoding against two different data sources in not a surprise to me. In my original reply I mentioned 'reputable data source'. That's a key element to geocoding.

Re: Different lat and long for same address

St_A — Wed, 29 Aug 2018 17:54:40 GMT

Much thanks for clarifying Joe!

Re: Different lat and long for same address

JoeBorgione — Wed, 29 Aug 2018 18:08:11 GMT

I used to work in a 9-1-1 call center that dispatched about 2,000 calls a day. The data I used to match against was constantly being updated for accuracy, and we had about a 99.5% accuracy rating; in 9-1-1 you need that, right?! Those data sources were fantastic, but took a ton of work to maintain for that sort of performance. And, that's all I did.

A couple of anecdotes: Once a dispatcher told me we should use Google maps as the basis for dispatch. I told him that would be fine with this caveat: he use Google when dispatching to his mothers house, and my data when dispatch to my house.... Another dispatcher complained to me that "Google doesn't update their data like you do; Why not? What is their update schedule? "

Re: Different lat and long for same address

St_A — Thu, 06 Sep 2018 20:50:43 GMT

Thanks Joe! Your reply to the dispatcher made me laugh out loud. Use Google at your own risk lol. I badly need your kind of data sources but like you say it takes a lot of work to maintain that high accuracy. I get road data from the government but that is not without accuracy issues. I am looking for other data sources to supplement. How did you go about gathering and maintaining Reference data for such a high accuracy.

Re: Different lat and long for same address

JoeBorgione — Sun, 09 Sep 2018 13:26:41 GMT

I had a wonderful situation where the 9-1-1 center I worked for dispatched for a number of cities, and using an Enterprise GDB the city GIS people maintained thier 'piece of the pie' for street centerline data. It worked out really really well. The county in which we were all located has an excellent addressing department that maintains individual structure addresses as points so between the streets and address points, it was pretty bomb proof. All that data has been worked for a number of years; it's not like we just opened the box and there it was: Lot's of coordination between agencies with respect to naming conventions etc.