Create a Predominance Map in Just 30 Minutes

A predominance map helps represent geographical patterns by comparing multiple attributes (fields) from your data. By showing differences in value between many attributes, we gain new insights about how data might be grouped geographically.

In this guide we’ll show you how to create a predominance map in Azimap.  We’ll use a working example, creating a map of election results in UK by constituency.

Time to complete: 35 mins.

Tools required - LibreOffice Calc (download before beginning), Azimap

Contents

1.    Getting started

1.1  Download and extract files

1.2  Download LibreOffice Calc

2.    Editing the dataset

2.1  Add attributes using LibreOffice Calc

2.1.1      Decide on your new attributes

2.1.2      Define column structure

2.1.3      Formula for WINNER column

2.1.4      Formula for NUMVOTES column

2.1.5      Formula for PERCVOTES column

2.1.6      Final edits to dataset

3.    Creating your predominance map

3.1  Create a new dataset

3.2  Import your data

3.3 Create your map

3.4  Style your data

3.5  Set up layer interactivity ( Optional) 

1.    Getting started

1.1.  Download and extract shape file

Download the following sample files: Azimap_Election_2024_Complete[1] and extract the zip file to a folder. 

1.2.  Download LibreOffice Calc

Download this software now if you still need to.  We’ll be using it to create some extra attributes (columns) and perform some calculations on our dataset.

2.    Editing the dataset

2.1.  Add attributes using LibreOffice

Open the .dbf file "Azimap_Election_2024_Complete.dbf" with LibreOffice Calc.

Accept the default character set.

2.1.1.     Decide on your new attributes

We’re going to add three new columns (attributes) to the .dbf file.  This is because while we have all the raw data, we want to use the data to create attributes (columns) that will translate easily onto a map. 

In this case, we’re going to create the following columns:

• Winner - the resultant elected party 
• NumVotes - the number of votes the winner achieved
• PercVotes - the percentage of the votes cast the winner achieved

2.1.2.     Define column structure

We now need to define the column structure, so each new column header should be set as:

WINNER,C,254 - varchar, 254 characters

NUMVOTES,N,10 - number 10 digits

PERCVOTES,N,10 - number 10 digits

Your new column headers will look something like this:

NB. Care must be taken that the data inserted in the created columns matches the above structure.

2.1.3.     Formula for WINNER column

In the WINNER column ROW 2, use the formula:

Here we are trying to return the column header to the cell of the highest value in the range. To do this we can apply a combination of INDEX, MATCH and MAX functions to get the result. 

We want to make the index range static rather than relative for this so select the first:

and press F4 which will make it static, like this:

2.1.4.     Formula for NUMVOTES column

In the NUMVOTES column ROW 2 use the formula:

This will select the highest number in the range.

2.1.5.     Formula for PERCVOTES column

In the PERCVOTES column ROW 2 use the formula

Right-click on the PERCVOTES column and choose FORMAT CELLS.  Set the column category to PERCENT and click OK.

Next, select all rows in the three new columns, except the headers. Use CTRL-D to copy the formula from the 1st row selected into all the other rows.

2.1.6.     Final edits to dataset

We’re nearly finished with the data work. Check that the values in the WINNER column display only the party abbreviation, such as LAB, CON, DUP or SF. The supplied DBF uses clean field names, so no further changes to the headings should be necessary. LibreOffice may display DBF field information such as LAB,N,10.

To return only the party abbreviation, the REGEX function removes the comma and the field information appearing after it.

=REGEX(INDEX($G$1:$S$1,1,MATCH(MAX(G2:S2),G2:S2,0)),",.*","")

Press Enter.

Check that the result now says something like LAB instead of LAB,N,10.

Select cells T2:T651.

Press Ctrl+D to copy the corrected formula down.

If LibreOffice rejects the formula, use the semicolon version:

=REGEX(INDEX($G$1:$S$1;1;MATCH(MAX(G2:S2);G2:S2;0));",.*";"")

Check the WINNER results

Check that the WINNER column displays only the party abbreviation, such as LAB, CON, DUP or SF. The updated formula removes the additional DBF structure information automatically. Do not change the party-column headers.

Save your amended file as a dBASE file (default)

That's it, all data preparation is complete – now let's make a map.

3.    Creating your predominance map

3.1.  Create a new data set

Click on Dataset section and select Create Dataset.

This will open up the first page of the map creation wizard.

Click the 'Create dataset' button to start creating a new dataset.

3.2    Import your Dataset

Click on Import. 

Click the 'Select files' button to choose a dataset file for upload and click Next.

Confirm your Import Options and click Next. 

3.3   Create your Map

Click the 'Create map from selected datasets' button to proceed with creating a map using the selected dataset.

Your map has been created!!

3.4    Style your data

The layer will load with the default polygon layer style (black outline, grey polygon).

Click the 'Add new style' button in the Styler panel to create a new style for the map layer.

Click the 'NEW STYLE NAME' field to enter a name for the new style.

Click the 'Create' button to finalize the new style named 'PredominanceTest'.

Click the 'Add' button in the Styler panel to create a new style.

Click the 'Polygon Thematic' option in the Styler panel to apply the thematic styling to the map.

Click the 'winner' option in the Column dropdown to set it as the data field for styling.

Change the style options as you see fit - I have set stroke width to 0.1 .

Next, click on the 2nd tab DATA RANGE to set the colours for your autogen style.

Click on the colour or enter your hex code to set to your desired colours.

After you have entered your desired colours, click the 'Generate' button to apply the current map layer settings.

3.5 Set up Layer Interactivity (Optional) 

Click the 'Adjust popup config' button to modify the popup settings.

Click on the  HOVER tab.

Choose the switch for the data you want to display in your interactive hover popup - I have chosen pcon24nm, winner and numvotes.

Click Save Changes

Now to see your new interactive popup, hover over any polygon.

Thanks for reading the guide and we hope you enjoy creating predominance maps with Azimap.