Guide
What is a postal address and how do you write one
An address looks like four fields to fill in. It is a sentence with a grammar, different in every country, that a person uses to find a door. This guide says what it is made of, why it goes wrong so often, what it means to put it right and what it means to verify it.
What a postal address is
A postal address is the route to a door: the country, the city, the street, the number on the street, and inside the building the staircase or the flat. Each part narrows the one before. That is why an address is data with a structure, and the structure is decided by the country's post.
National posts publish a composition standard: the order of the lines, what goes in capitals, where the house number sits, how to abbreviate. Sorting centres read the address with machines, and a line out of place or a generic postcode sends the letter on an extra trip, or back.
The parts of an address
- Street·a type (via, piazza, rue, straße, calle) and a name. The type can come before, after or attached to the name; the name can have particles (“de la”, “van der”) that stay lower case and abbreviations (“S.”, “G.”) that must be expanded.
- House number·a number, sometimes with a letter or a suffix (“7a”, “12/B”, “14-16”), in some cities with a colour (the red numbers of Genoa and Florence). It comes before or after the street depending on the country, and must never be confused with the staircase, the flat or the floor.
- Building·Staircase, flat, floor and building name: they sit inside the building, not in the street line, and every country writes them its own way. They stay next to the address, and where the register knows the units of the building the check confirms them.
- Postcode·identifies a delivery office, not a city: big cities have dozens, and in some countries the code identifies the stretch of street or the single building. It has a fixed form per country: five digits, four digits and two letters, two groups with a space or a hyphen.
- City·the municipality, in capitals and in its official name. The hamlet, the district or the arrondissement are extra information: they go in their own place, and the locality stays the municipality.
- Province or region·where the country uses it in the address: the province code in Italy, the state in the United States; in Germany, France or Spain it is not written.
- Country·the last line, in capitals, in the language of the sender; the prefix in front of the postcode (D-, F-, CH-) is an outdated custom and is removed.
Why addresses go wrong
Addresses go wrong because people write them, in a hurry, each in their own way. The mistakes are always the same, and they can be recognised.
- Abbreviations: “v.”, “p.zza”, “str.”, “avda.”, “gt.”. Whoever writes them understands them; a machine does not, and two records of the same person are not recognised.
- Generic or old postcode: 20100, 00100, a code from before a reform. The letter reaches the wrong office.
- Hamlet instead of municipality, or the other way round: the locality written is a district, an absorbed village, an industrial area, and the municipality is unclear.
- Things out of place: “c/o”, staircase, flat, floor and building name inside the street line, which becomes unreadable.
- City in another language: Munich for München, Lisbon for Lisboa, Antwerp for Antwerpen. The post of that country wants it in its own name.
- Right street, non-existent number: the mistake no rule of form can see, and only the address register can tell.
Normalising and verifying: two different things
Normalising an address means rewriting it in the postal form of its country: postcode in the right format, abbreviations expanded in the local language, capitals as customary, house number where it belongs, city in its local name, whatever does not belong moved to its own place. It can be done for every address in the world, because the form is a rule.
Verifying an address means checking it against the national address register: does that street exist in that municipality? does that house number exist on that street? is that postcode its own? It can only be done where the register is published and in service, and it adds the coordinates of the house number. An address can be normalised without being verified; the outcome always says which of the two was done.
A badly written street is found again in the country's register: a typo, an abbreviated street type, words in another order. If the correction is clear-cut it is applied and declared; if more than one street is possible they come out as suggestions and the address stays as it was written.
One rule applies to both: every change is declared, and what is not known is not invented. An address that cannot be reconstructed with certainty comes out with the reason.
What changes from one country to another
Every country has its own grammar. The countries whose register is in service, each with its page:
| Country | House number | Postcode | Register |
|---|---|---|---|
| Italy | after the street | 12345 | every municipality |
| Germany | after the street | 12345 | 16,751,744 house numbers |
| France | before the street | 12345 | 26,065,344 house numbers |
| Spain | after the street | 12345 | 15,428,192 house numbers |
| Netherlands | after the street | 1234 AB | 10,066,060 house numbers |
| Portugal | after the street | 1234-567 | 2,621,732 house numbers |
| Belgium | after the street | 1234 | 5,515,623 house numbers |
| Switzerland | after the street | 1234 | 3,267,455 house numbers |
| Liechtenstein | after the street | 1234 | 12,733 house numbers |
| Czechia | after the street | 123 45 | 3,022,218 house numbers |
| Denmark | after the street | 1234 | 2,616,162 house numbers |
| Norway | after the street | 1234 | 2,570,525 house numbers |
| Finland | after the street | 12345 | 5,263,747 house numbers |
| Austria | after the street | 1234 | 2,511,669 house numbers |
| Slovenia | after the street | 1234 | 655,767 house numbers |
| Luxembourg | before the street | L-1234 | 179,184 house numbers |
| Hungary | after the street | 1234 | 736,062 house numbers |
| Romania | after the street | 123456 | 1,026,122 house numbers |
| Ireland | before the street | D02 X285 | 552,435 house numbers |
| Slovakia | after the street | 123 45 | 1,896,376 house numbers |
| Iceland | after the street | 123 | 231,686 house numbers |
| Croatia | after the street | 12345 | 1,682,480 house numbers |
| Greece | after the street | 123 45 | 1,411,296 house numbers |
| Andorra | after the street | AD123 | 343 house numbers |
| Monaco | before the street | 12345 | 352 house numbers |
| San Marino | after the street | 12345 | 11,495 house numbers |
| Vatican City | after the street | 12345 | 130 house numbers |
For the other countries the postal form of the country applies: postcode, abbreviations, capitals, house number, country line. The list grows with the registers: all countries.
Coordinates and precision
A verified address has a point on the map: latitude and longitude of the house number, taken from the national register. When the exact number is not there, the point is estimated between the neighbouring numbers on the same street; when even that is missing, it falls back to the point of the street or the centre of the municipality. The precision field always says which level was reached — house number, interpolated, street, municipality — so whoever uses the coordinates knows how much to trust them.
Where the national register does not publish an area, the point may come from OpenStreetMap: in that case the source is declared and the attribution must be reproduced if the coordinates are published.
What happens to a file
A file of addresses — customers, donors, members — is almost always dirty in the way described above, and the dirt does not show until the letters come back. Uploaded as it is, it comes back with an extra column for each field fixed and a column with the outcome: correct, modified with what changed, to be checked with the reason. The columns that have nothing to do with it stay intact, in their original order.
You can upload CSV, Excel, LibreOffice, JSON or XML. If the file has no country column, choose the default country before starting: it only applies to the rows that do not declare one.
The rows to check are usually few, and they are the ones no rule can decide: a street not found in the municipality, a house number that does not exist. There a person is needed, and the outcome lines them up. How to prepare the file is on this page.
Addresses and duplicates
The same person at the same address, written in two ways, is the most common duplicate in a contact list, and the hardest to see with a spreadsheet: “v. Leopardi 4” and “Via Giacomo Leopardi, 4” are different strings. Normalising the addresses before the comparison collapses the two spellings onto the same form; for foreign addresses a comparison key does the same job in the country's language (“350 Fifth Avenue” and “350 5th Ave” match).
Then the comparison looks at the name — nicknames, initials, surname and first name swapped, typos — and the contact details, and gives a level of certainty for each group. How it works is in deduplication.
Frequently asked questions
How do you abbreviate the word “address”?
The usual abbreviation is “addr.”; on forms you will also see “add.”. On the envelope the word is not written: the line with the street and number is enough. Abbreviations inside the address (“St”, “Rd”, “Ave”) are a different matter: they follow the rules of each country’s postal service, and verification spells them out where the register writes the street in full.
What is the difference between normalising and verifying an address?
Normalising means writing it in the postal form of its country: postcode in the right format, abbreviations expanded, capitals as customary, house number in the right place. Verifying means checking it against the national address register: that street exists in that municipality, that house number exists on that street, that postcode is its own. The form can be given to every address in the world; verification only where the register is in service.
Is a normalised address necessarily correct?
No. An address can be perfectly written and not exist: a street that is not in the municipality, a house number never assigned. That is why form and verification are two different things, and the outcome says which of the two was done.
Why is a generic postcode not enough?
In the big cities the postcode changes from one street to the next, and sometimes along the same street. A generic code (20100 for Milan, 00100 for Rome) is accepted by forms but does not identify the delivery office: the letter takes an extra trip, or comes back.
What happens if an address cannot be verified?
It stays in the country's postal form, with an outcome that says why: street not found in the municipality, house number not found, insufficient data.
Do verified addresses have coordinates?
Where the national register has them, yes: latitude and longitude of the house number. When the exact number is missing, the point is estimated from the neighbouring numbers or falls back to the street or the municipality, and the precision field says which level we reached.
Verify an address
One address at a time from the site, a whole file from your account area, or the API inside your application.