Streets & Trips
I noticed that in the state of IL, the GPS location is off by 15 - 45 miles hence making the Gas Finder useless because I would have to travel 15-45 miles to a location because the zip is wrong no matter which city I am in. A quick fix is to enter the zip code manually but there are some cities I don't know the zip code.
I noticed the Zip.dat file but does anyone know a quick way I can fix the coordinates (longitude & latitude) to reflect the city I am in. This doesn't affect IG3 as it displays properly.
I have found the zip code information to be somewhat unreliable also. Obviously, this has to do with the quality of the database rather than programming. Unfortunately, I don't know how to update the database.
The idea is to fix or re-create the zips.dat file with the correct coordinates the GSP satellites use.
Unfortunately you are not going to get 100% accurate information from a database like this. There are no "boundry lines" between zipcodes, as you would see on a map for instance. It works off of a circular radius. This means these "circles" can overlap. The database does the best job it can, with only 2 coordinates, to give you a general idea of where you are.
What you can do, is say you are at home, and it shows you in another zip, get the lat and lon for your location, and put it in the zips.dat file next to where it is showing you are by searching for the zipcode in the database. It will the see that you are closer to your new coordinates that you put for your area, than the previous ones, and return the correct area.
Again, this is based on a circle, so if you drive 5 miles down the road from your house now, and are supposed to be in a new zip, you still may be closest to the one you just created, and thus, now display the wrong information again.
The only way to improve the accuracy, is to have many, many, Lat & Lon's for an area, say like a mile apart. This will still not be perfect, but will significantly increase the accuracy. Problem is, to do that on a national scale, like this database is, would make the file size almost unmanageable.