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What is a Geocoder?

M. Haskins
M. Haskins

Geocoding refers to the conversion of a physical address, such as a street address, to geographical coordinates, commonly longitude and latitude, to display the location on a map. Reverse geocoding does the opposite calculation and finds a street address when given a set of geographical coordinates. A geocoder, or geocoding system, is a piece of software or a web service that performs geocoding. A geocoder can be used for various purposes, for example getting directions, cartography, and geotagging. Geotagging involves adding a geotag, which is geographical data like latitude and longitude, to various kinds of media like photos, videos, RSS feeds, and websites.

The three most common methods of geocoding are: by address; by postal code, ZIP code, or the local equivalent; and by boundary. When geocoding by address, a geocoder commonly uses a reference file with data such as street addresses and street names that have already been mapped. It then matches the data in the reference file against the list of addresses it is geocoding. Often a process called address interpolation is used to estimate the position of a specific address, meaning the system estimates where a specific address is located based on the general information in the reference file. For example, a geocoder can figure out at which end of a block or street an address is located based on the range of building numbers, or what side of the street a house is located on based on whether the building number is odd or even.

Man holding computer
Man holding computer

Using postal codes can be problematic, especially in rural areas where each postal code covers a very large area. In urban areas, this method is more accurate because each postal code covers a much smaller geographical area. Geocoding by boundary is the least reliable method, because it will only show a general area where a specific address is located.

There are difficulties with all methods of geocoding. Even the most reliable method, using physical addresses, has its problems. For example, new addresses may not have been added to the geocoder's database yet or streets may have the same name but are located in different geographical areas. There is a wide range of geocoding systems available and some are free to use, while others require a licensing fee. Some examples of geocoders are the relatively well-known Internet-based services like Google Maps, Yahoo PlaceFinder, and USC Geocoder, and systems like Geohash, C-squares and ISO 6709. There are also text-based alternatives that do not require the user to be online.

Discussion Comments


@pastanaga - Well, unfortunately there's not much you can do about it. Every cell phone with any kind of GPS chip is almost certainly transmitting information about you to a geocoding service that summarizes your movements to advertisers.

There are already patents out on ads that would be geolocated, so that you get a voucher to Starbucks in your phone when you walk past it in the street.

There's just no way to stop it if you want to use the technology for your own aims. The only positive spin I can give it is that the amount of information is so enormous that I don't think individuals have to worry about anything more than irritation. Starbucks doesn't care, for example, if you just walked past your ex's house for the fifth time to spy on him. They only want to sell you coffee.


@browncoat - See, that's one of the things that worries me about geocoding software and how easy it is for everyone to tag information in the real world now. It has a lot of good implications, too, but it can be so easily used to invade people's privacy.

I mean, that sounds like they've basically associated people with their location and their DNA. What if Hitler had that kind of information? Or any other genocidal dictator? What if even a skinhead or some other kind of racist person gets hold of it?

Even if you don't go that far, what if an insurance company gets hold of the information and cross checks all their addresses against genetic data to decide whether they will cover people.

Linking anything with an address or location is so incredibly dangerous these days.


One of the most interesting versions of this I've seen is what they offer at a DNA sequencing business. I haven't had it done myself, but I've seen what another woman found out and they basically show her a map with all the other people that have been sequenced and how related she is to them.

So, it looks like a geo-tagged map, with each tag representing where a person lives and marked with "second cousin" and so forth on it.

I just think it's pretty amazing that they can figure that kind of stuff out!

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