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Place-name choropleths

Revision as of 11:55, 2 June 2019 by Henryfunk (talk | contribs)
Viewing choropleth • View choropleth • View choropleth • About the choropleths. County boundary data provided by the Historic Counties Trust.

By Henrik Thiil Nielsen, 2017-11-06. Revised by Henrik Thiil Nielsen, 2019-06-02.

This page includes choropleth maps of the English counties, detailing the geographical distribution of Robin Hood-related place-names and localities from three different perspectives. The dataset on which they are based is set out in a table below.

The choropleths

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 for statistical purposes assigend to Yorkshire.

Simple county count

For the first map, 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

For the second map, 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 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 third choropleth attempts to take area as well as population density into account. Here we first calculate an expected place-name count 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 the preceding maps.

Notes and caveats

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. Sometimes for a day or two the colour codes on the maps may be out of sync with those listed in the table. In such cases those in the table are the correct colours.

Colour codes

On all three maps, 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 map is given below. Population and area data for England and its 39 historical counties are taken from the first (1801) census.[2]

Limit (index)Colour
Less than 10
Less than 20
Less than 30
Less than 40
Less than 50
Less than 60
Less than 70
Less than 80
Less than 90
Less than 100
Less than 110
Less than 120
Less than 130
Less than 140
Less than 150
Less than 160
Less than 170
Less than 180
Less than 190
Less than 200
Less than 300
Less than 400
Less than 500
Less than 600
Less than 700
Less than 800
Less than 900
Less than 1000
Less than 1500
Less than 2000
Otherwise

Dataset

Click header to expand dataset for England or each county/shire.

Background

Notes