The maps, if available, show both where there are more people named Riordan and where they are most concentrated.

The distributions are shown by means of coloured dots centred on the various British counties. The dots relate to the county as a whole, not to any specific location within the county.

For the 1881 census, the counties used are those which existed at the time and were recorded on the census data. For the 21st century stats, the traditional or ceremonial counties are used in order to avoid distortions caused by unitary authority cities.

The darker the colour, the more people in that county are named Riordan.

The larger the dot, the greater the proportion of people in that county are named Riordan.

Hovering over the dots will give you the individual statistics for that county.