If you’re going to stay in Spain long term then you really need to get yourself registered on the ‘padrón’ (population census).
This is important for a number of reasons; firstly you’ll then be a legal resident in the city and secondly this will allow you to sign up for a number of services such as private health insurance, gym memberships and phone contracts. What’s more, the government uses the data from the padrón to allocate funding to towns and cities for new and exciting projects we can all benefit from.
Luckily this is a fairly straight-forward process. The biggest and most convenient office to go to is located just off Plaza de la Merced (Calle Merced, 1), above the gourmet market. Follow signs for ‘padrón’ or ‘empadronamiento’ to the appropriate office (on the first floor) and take a ticket and wait to be attended.
Once your number is called, inform them that you would like to ‘empadronarse’. They will give you a simple form to fill in and once you return it, along with several copies of the documents it specifies (NIE, passport etc.), they will send it off and you will receive a letter from the mayor welcoming you to the city.
This can take up to two months but is often much quicker. If you return to the office a few days later they can tell you if your application is successful and print you off a certificate (if your situation is more urgent).
If you need to change your address at a later date, the process is the same but the form slightly different.
UPDATE: Those applying for a TIE (non-EU) and need to get on the ‘padrón’, can identify themselves using their passport.