So you're looking for a friend who lives in Douglas Road in London. OK, there are 18 of them, so which one is it? There are hundreds of cases like this in London.
What you need is a postcode and preferably a full postcode, as you may find two streets of the same name in the same postcode area.
N is North, E is East, SW is South West. SW1 is the first subdivision of twenty of the South West postcode area. Each one is vast in size.
Each subdivision is therefore further divided into smaller areas, with a number and two letters (SW1 4DL), identifying a part of a street or estate.
In or near the City of London the postcodes are WC or EC and a further letter is sometimes added to the first part of the postcode (WC2R 2PP).
When Londoners talk about London areas they often identify them by their postcode, for example, "I live in N1 and work in WC2."
Most postcode areas have at least one Tube station or National Rail (NR) station, but some have many.
You can check it out on the web at: http://www.streetmap.co.uk/
Royal Mail Postcode Guide 0906 3021222, 08:00 - 18:00 weekdays (Calls charged at 50p/min).
08457 111 222 18:00 -20:00 weekdays, 09:00 - 17:30 Saturdays (Calls charged at local rates)