Place-name choropleths
By Henrik Thiil Nielsen, 2017-11-06. Revised by Henrik Thiil Nielsen, 2022-05-27.
This page includes a choropleth map of the English counties, detailing the geographical distribution of Robin Hood-related place-names and localities from three different perspectives. The choropleth can also be selected via a button below the map found in the top right corner of all those landing pages in IRHB's place-names section that deal with English place-names. From links in the text below the choropleth it is possible to switch between three modes: Count, Area, and Area/Population. Below is found discussion of these choropleth views, a list of colour codes and a table containing the dataset on which the views are based.
The choropleth
A choropleth is something much more widely known than its name: a "thematic map in which areas are shaded or patterned in proportion to the measurement of the statistical variable being displayed on the map".[1] It thus resembles a heat map, but unlike a heat map in which variation is in principle continuous, it displays data averaged over discrete geographical regions, in this case the English historic counties.
While Robin Hood-related localities in Greater London can be found on the London place-names page, for the choropleths they are assigend to the historical counties under which they belong, i.e. Essex, Kent, Middlesex or Surrey. Similarly, localities listed under the three historical ridings of Yorkshire are all assigend to Yorkshire here.
Simple county count
In Count view, the count of English place-names and localities currently covered on IRHB is divided by the number of historic counties. This figure is set to index 100 and used as the base for calculating the indexes for individual counties. Counties with an index value between 100 and 109 (both inclusive) are shown in white, those with higher values in progressively darker shades of green, those below 100 in increasingly dark shades of red. Since the counties vary so widely in size, we are here, as it were, comparing gooseberries to water melons and fruits of all sorts of intermediate sizes. Yet the main tendencies recur on the two following, more meaningful representations of the data.
Taking area into account
In the Area view, the density of Robin Hood-related place-names and localities in England – expressible as area in km2 per place-name or vice versa – is taken as index 100 and indexes are calculated for individual counties based on their areas and counts of relevant localities/place-names. Colour gradation as on the first map.
Taking area and population into account
The Area/Population view attempts to take area as well as population density into account. Here an expected place-name count is first calculated for each county based on its area and the average count per km2 for England. On the basis of the population densities of England and the county in question we then adjust the expected figure upwards or downwards to reflect the population density of the county. This is done in linear fashion. The result is used as index 100 for the county, whose index value is then calculated on the basis of the actual count of place-names/localities. The colouring thus reflects the extent to which expectation is exceeded (or the opposite). It is an open question whether a statistician would find this procedure reasonable, but it obviously takes people to give places names, and it seems a reasonable assumption that population density has at least some influence on the density of named localities in a given area. It seems doubtful if this effect is linear, but without any relevant empirical knowledge, any adjustment that could be made to the way in which it is factored in would be arbitrary. Colour gradation as on preceding maps.
A caveat
Keep in mind that the choropleths reflect the current state of affairs at IRHB. An estimated 200 place-names are still to be entered. Many of these, mostly of fairly recent origin, belong in the counties that are currently red on the maps.
Colour codes
In all three views, a tri-polar colour progression is used, counties with values above the mean – set to index 100 – being coloured a progressively darker green, while those below are coloured a progressively darker red. Areas with values close to the mean are white or nearly so. Ideally colour gradation should be linear, but since there are a few important outliers in the data, this could only be achieved with colour steps so small that they become difficult to discern or, on the other hand, such large intervals of values grouped together that resolution for values closer to the mean would be insufficient. Intervals are therefore larger for areas well above the mean. A brief description of each view is given below. Population and area data for England and its 39 historical counties are taken from the first (1801) census.[2]
Dataset
Click header to expand dataset for England or each county/shire.
Background
- Histpop – The Online Historical Population Reports Website: Population tables I, Vol. I. England and Wales. Divisions I-VII, 1851 – Page clxviii (University of Essex)
- Wikipedia: Choropleth map
- Wikipedia: Heat map.
Notes