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 map

3.2  Upload your data

3.3  Style your data

3.4  Set up layer interactivity

1.    Getting started

1.1.  Download and extract shape file

Download the following sample files: UK Elections Results 2015.zip [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 "GB&NI_Election2015.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!  As you can see from the above screenshot, unfortunately LibreOffice Calc copies the structure information of the header into the winner column. To solve this, delete the structure data from the applicable header cells (don't worry this is only visual).

Change your headers from this:

To this:

Result:

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 map

Click on MAPS section and select CREATE MAP.

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

Name your new map and select NEXT.

3.2.  Import data and add to map

At this stage you have a number of options. You can create a brand new layer for your map by selecting the CREATE LAYER button.  Alternatively you can choose to upload one or many of your existing layers onto your map (your full list of layers will appear), or you choose to create an empty map.

When you try to load a map without any layers attached you will get the below warning.

In this case however, we'll choose the CREATE LAYER button (this is also accessible on the map using the gears button on the layer tree view).  You'll be prompted with the below pop-up.  Select YES, GO.

Re-zip the shape file (as it’s quicker to upload) and drag and drop to upload.

Rename your layers after upload if you desire (upload may take a little while depending on internet speed).

Click SAVE to import (should take around a minute)

3.3.  Style your data

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

Click on the style preview icon next to the layer name in the layer chooser to modify the style.

Click NEW to create new style.

Click ADD and choose the POLYGON THEMATIC STYLING wizard.

Select the attribute you want to style against - for this map we will use the earlier created column "Winner".

Change the style options as you see fit - I have set stroke width to 0.1 and stroke opacity to 50%.

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 OK to exit.

If you’re happy with the style, click SAVE. Click YES to save as current style or NO to give the style a new name.

This will reload the layer with the new style and should look like below.  Well done you've got a predominance map!

3.4.  Set up layer interactivity (optional)

Azimap has the capability to add client-side interactivity to a map layer utilising UTFgrid. Just choose the data you want to show on hover, and it will display on the map immediately.

Select the edit map layer config button in the layer chooser control (the gear symbol).

This will open the map layer config. control.

For this map click the CONFIGURE HOVER/CLICK POPUPS button.

Select the 2nd tab HOVER - here we can choose the styling of our interactive popup (black theme/ white theme or data layout of horizontal or vertical).

Choose the switch for the data you want to display in your interactive hover popup - I have chosen CONSTITUENCY, WINNER and NUMVOTES. Click OK and then Click SAVE.

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.