Neither by district nor by neighbourhood: two cartograms so that the election maps do not lie to you

This is a translation of an original article published at Catalunya Plural in Catalan and Spanish.

Barcelona en Comú won 6 of the 10 districts of the city. Esquerra Republicana has done so in 30 of the 73 neighbourhoods. But election maps showing the winner by area often hide a more complex reality. We show two maps that adjust the sizes of their areas to its population and their colours to the percentage of votes to see how the parties are distributed in Barcelona

On Sunday night, when Ernest Maragall’s victory in Barcelona was already public, with 4,833 votes ahead of Ada Colau, there were lots of maps around social networks showing that the current mayor had won in 6 of the 10 districts of the city. This media also published this map, as it was the most detailed data available at that time.

Some Twitter users members or related to Barcelona en Comú [BeC, Ada Colau’s party] retweeted this map. It is true that, if we talk about districts, BeC achieved a highest percentage of the votes in a majority of districts: Ciutat Vella, Gràcia, Horta-Guinardó, Sant Andreu, Sants and Sant Martí. ERC was first in only two districts (Eixample and Les Corts), PSC in one (Nou Baris) and BCN Canvi – Cs in 1 (Sarrià-Sant Gervasi).

But city results were tight. Between the two first parties there was less than a percentage point in terms of percentage of votes — ERC won with 21.35% of the vote, ahead of 20.71% of the votes for BeC. So as of Monday, when more data became available, ERC counterattacked by showing the map of Barcelona by neighbourhoods, where ERC’s yellow predominated. They won in 30 of the city’s neighbourhoods, while PSC won in 24, BeC in 14 and BCN Canvi – Cs in 5.

While both the largely purlple — districts — and mostly yellow — neighbourhoods — map are true, maps are not always the best way to convey information. Under the guise of objectivity, maps can distort results because they are more accurate in terms of geography, but not in terms of inhabitants.

In an electoral system like ours, the vote of every Barcelonian is the same, but not all neighbourhoods or districts have the same population. That is why painting the colour of the winning party in each district or neigbourhood to show who has won is misleading. These maps can be useful to see geographical trends but not to sum areas and quantify each party’s profits.

An alternative to traditional maps are cartograms, which adjust the size of territorial areas to the number of people who inhabit them. In the map below, for example, we can see that the importance of winning in the Eixample — which has 260,000 inhabitants — is not the same as winning in Les Corts — which has 80,000.

In addition, maps that show only the winning party can be useful in cases where the winner takes it all (as in the US or the UK), but in the case of our electoral system they hide all the votes that equally add to the rest of the candidacies. For example, in Ciutat Vella, BeC was almost seven points above ERC (27.5% against 20.7%), but in Gràcia the difference was less than a percentage point (23.83% of the votes for BeC and 23.76% for ERC).

To try to better illustrate these differences, in the following chart the colour of the winning party is more or less intense according to the percentage of votes that party has obtained in that district.


Interactive cartogram in the original article

The same thing happens when we show the neighbourhoods relative to their population. For Esquerra it is much more important to win in Nova Esquerra de l’Eixample, which has almost 60,000 inhabitants, than in Vallvidera which, despite occupying a huge area, does not reach 5,000 inhabitants.

Likewise, the victory of Barcelona en Comú to Sant Andreu, with 57,000 inhabitants, has a much greater influence on the final result than it’s winning of La Clota, a district in which just over 600 people live.


Interactive cartogram in the original article

The intensity of the colors in this map also helps us to see that the clearest wins by neighbourhoods are precisely those of PSC in several neighbourhoods of Nou Barris, such as Ciutat Meridiana, Torre Baró or Roquetes, and those of Barcelona pel Canvi — Ciutadans at Pedralbes and Tres Torres. Both parties have won more than a third of the votes in these neighbourhoods, where they have the second most-voted party at more than 10 points.

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