Where personal information and web technology collide, so privacy concerns inevitably surface.

The Met's new crime mapping site is the latest in a line of services to raise disquiet in the Information Commissioner's Office - which is charged with safeguarding privacy.

The ICO's particular concern is that by learning the exact whereabouts of a crime, an observer may then - by deduction and a little further research - ascertain the identity of the victim of that crime.

For instance, if I knew the street - or indeed street address - of a burglary, I could - with some searching in the electoral roll and door-knocking - find out the name of the victim.

The Met has got around the ICO's concerns by making the crime 'hotspots' marked on its maps less specific; instead of being linked to an individual street - let alone an address - crimes are now mapped to an area of 'six streets', which the ICO has declared ensures sufficient anonymity for victims.

What is interesting about the Met's new crime map is that it is one of the early examples of what will undoubtedly become a much more common use of 'personal information' on the web: namely aggregating such information to create highly compelling services. (In the technology industry, such services are known as 'mash ups'.)

To date there have been two main sources of concern when it comes to privacy on the web. The first stems from when we give personal details to someone providing a service over the web who then either misuses that information or loses it.

In this category you could heap everything from a website providing details of your age and address to an advertiser or other marketing company without your consent, to an online retailer which lost its credit card and other financial details.

The second is the much-publicised posting of personal details on social networking sites such as Facebook - often without the subject's consent - which can then be scrutinised by potential future employers and anyone else with access to such sites.

The Met's service is one of a new breed: where a huge database of information, including details that may or may not identify individuals - is blended with another source of information, like a map, to create a previously unavailable service - in this case, the ability to find out 'which crimes are committed near me'.

One much-talked-about example of such services is a US site called EveryBlock, which takes information from a whole range of publicly available sources - property records, crime statistics, and local authorities - and maps them according to geography.

The idea is that someone using the site can create 'a news service for their postcode'. "If someone lodges a planning application for the apartment below yours, that wouldn't be generally be considered news, but it's news to you, and at present there isn't an easy way of getting access to that information," the site's founder has said.

In many instances, information available on such 'mash ups' will not identifiy individuals, but there may be ways of using details they contain to make identifications - as was the concern in the Met's case.

As more, similar services are rolled out in the UK, it will become increasingly difficult for the ICO to monitor them all and ensure each is abiding by the terms of the Data Protection Act.

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