A national identifier, when contained in an ID card, can enable information about a person that is stored in different databases to be easily linked and analysed.
 
ID cards have become 'smarter' due to the availability and lowered cost of tiny microprocessers which can store a large amount of data. This technology allows multiple applications to be stored on the same national ID along with a personal identifier (such as a password or biometric identifier). Finland, Malaysia and Singapore have experimented with 'smart' ID cards.
 
Such systems are easily contrasted with, for example, the Portugese system. Although Portugal has an ID card scheme, their cards do not connect to databases of information and are purely 'on-the-spot' cards. 
 
'Biometrics' are a key part of the ID card debate in Britain. The term 'biometrics' refers to the identification or verification of someone’s identity on the basis of physiological or behavioural characteristics. Fingerprinting is the best known and established type of biometric testing. Also, retina or iris scans, hand geometry, voice recognition, and digitised images.
 
A biometric system involves comparing a previously captured  characteristic of a person to a new sample provided by the person. This information is used to verify that a person is who they said they were (a one-to-one match) by comparing the stored characteristic to the fresh characteristic. It can also be used for identification purposes where the fresh characteristic is compared to all the stored characteristics (a one-to-many match).