Lat and long for an address: find the town, check the pair

You have an address and want its latitude and longitude. The latitude and longitude finder knows towns and cities, not streets: “10 Downing Street, London” finds nothing. What do you type, and how do you know it is right? Type the town alone, take the row whose region and time zone match, then check the pair backwards and by distance.

The pair you get is the town’s point, not the building’s. Wikipedia puts Downing Street at 51.5033, -0.1275, and the reverse lookup finds London’s point 0.6 km from there. That is close enough for a time zone, a chart or a distance between towns, not for a delivery.

What do I type for an address?

The town or city on its own, spelt as the finder’s list spells it: no street, no postcode, and no state after a comma. “Downing Street”, the postcode “SW1A 2AA” and “Paris, Texas” all find nothing.

Spelling counts. “Lisboa” and “München” find nothing, while “Lisbon” and “Munich” do. The name matches from its first letters, so “Saint Louis” brings up Saint Louis Park, Minnesota, and the Missouri city answers to “St. Louis”.

The list stops at twenty places, most populated first, so a small namesake can fall off it. “Paris” fills all twenty rows with the French capital and its districts, and Paris, Texas, is not among them.

Which row is the address’s town?

The row whose region code, country and time zone match the address; the first row is only the most populated place with that name. “Springfield” returns fourteen places in the United States and Australia, led by Springfield, Missouri, with 170,188 inhabitants.

An address in Springfield, Illinois, wants the third row, marked IL, US and America/Chicago. The time zone separates namesakes too: Springfield, Massachusetts, second on the list, runs on America/New_York.

The region code comes from GeoNames, the public gazetteer behind the finder. It is the state’s two letters in the United States and ENG for England; most other countries have a code such as 14, the Lisbon district.

How do I check a pair with the reverse lookup?

Paste it into Latitude and Longitude under “A point instead of a name”, leave the place name empty, and the address’s town should come back among the five nearest places. The pair the finder gives for Springfield, Illinois, comes back as Springfield, 0.0 km away.

A pair typed the wrong way round lands somewhere else entirely. Lisbon’s pair entered as latitude -9.1498 and longitude 38.72509 comes back as Kilwa Masoko, Tanzania, 90.1 km away, in the Africa/Dar_es_Salaam time zone.

What does “Distance to” tell me about a pair?

Put a place whose distance you already know in “Distance to”, and a wrong pair shows as a wrong distance or a wrong direction. The field takes a town’s name or a “latitude, longitude” pair, and measures from the top match.

With Lisbon as the place name and Lisbon’s pair without its minus sign, 38.72509, 9.1498, the answer is 1,584.8 km on an initial bearing of 84.2°, east. A dropped sign on the longitude moves a point east or west along its latitude.

Distance also tells namesakes apart. From the top Springfield, in Missouri, Chicago is 706.9 km away; from the Illinois one, 282.9 km. If you expected about 280 km, the top match is not your town.

A name typed in “Distance to” goes to the most populated place that starts with it, so give a namesake as its pair.

Questions

What does “No place found for this search” mean?

No place in the gazetteer starts with what you typed, or, for a point, no town lies near enough to list. Shorten a name to the town alone, in the spelling the list uses.

Is 0, 0 a real location?

It is a point in the Gulf of Guinea, roughly 600 km south of the West African coast according to Wikipedia, and the reverse lookup finds no town near it. Its nickname, Null Island, is often used in mapping software to find records wrongly given 0, 0.

Why does my phone give a different pair for the same address?

Your phone reports where you stand; the finder gives one point for the whole town. The two can differ by up to the size of the town, so check a phone’s pair with the reverse lookup rather than digit by digit.

Sources and further reading

• GeoNames export readme — what the region codes are: ISO codes for the United States, FIPS codes for most countries, an extra level for the United Kingdom.
• 10 Downing Street — the coordinates used for the address example.
• Null Island — the 0, 0 point, its distance from land, and the records wrongly given it.