**Boroughs**

London is divided in to 32 boroughs each aligning with local council boundaries.

**Wards**

Each borough in London is subdivided into around 20 electoral wards, 629 in total.

**Sub-wards**

Sub-wards are the smallest areas shown on the map. Sub-wards are known formally as lower super output areas (LSOA), with an average of 633 households.

**LSOA**

A Lower Super Output Area (LSOA) is described on the map as a sub-ward and is a pre-defined area consisting of an average of 633 households. In the MPS there are 4,829 LSOAs which are described on the map as sub-wards, For more information please refer to the Office of National Statistics.

**Standard Deviation**

Standard Deviation is quite a complicated concept and involves using a mathematical formula to calculate what the standard deviation is for any particular set of data. Standard deviation is a measure which can tell you how spread out figures in a set of data are from the average or "mean".Where the standard deviation is large the data will be spread out widely and where it is small the data will be clustered more closely. A standard deviation figure can also be used to help describe how far from the "mean" or average a particular part of a set of data is (i.e. within one, two or three standard deviations).

**How is standard deviation applied to crime rate?**

For example, if a city had six boroughs each with populations of 1000 but which had between them 6, 8, 9, 11, 12 or 14 crimes in a month, the "mean" or average crime rate for the city as a whole for the month would be 10 crimes per 1000 people. Using a standard deviation formula this city would have a crime rate with a standard deviation of 2.9 and most boroughs (in this case four) would have crime rates within one standard deviation (below 12.9 or above 7.1) and be classed as average. Two boroughs would have crime rates outside one standard deviation but within two standard deviations (above 12.9 but below 15.8 or below 7.1 but above 4.2) and would be classed as either above or below average.

**What is the formula for standard deviation?**

To calculate standard deviation you must square (multiply by itself) the amount each borough's crime rate differs from the city's mean crime rate and add these figures together (giving a figure of 42 in the example above). This figure must then be divided by one less than number of boroughs (giving a figure of 8.4) and the square root of this number established. This final figure (2.9) is the standard deviation.

**National Census**

The National Census is a survey of all people and households in the country. It provides essential information from national to neighbourhood level for government, business, and the community. The most recent census was on 27 March 2011.

**Notifiable Offence**

A Notifiable Offence is any incident where the police judge that a crime has occurred. Not all incidents that are reported to the police result in a crime.