How to Join Two Layers

In this guide we’ll show you how to join two layers.  To join 2 layers, your layers will need a shared attribute. 

We’ll use a working example of US election data.  The zip file below contains a US counties Shape file and a CSV file containing 206 US election results.  The datasets contain a shared column for fips county code, allowing them to be joined into a new dataset by adding the data columns from the CSV to the geometry data in the Shape file.

Time to complete: 20 mins.

Files required: Election data and US Counties Data**

Contents

1.    Getting started

1.1  Create map

1.2  Download data

1.3  Import data onto your map

2.    Join your data

2.1  Using the join data tool

2.2  Preview joined data

2.3  Save your new layer

3.    Style your new layer (optional)

1.     Getting started

1.1.  Create map

Create New Map.

1.2.  Download data

Download data from Election data and US Counties Data.

The zip file contains a US counties Shape file and a CSV file containing 206 US election results.  The datasets contain a shared column for fips county code, allowing them to be joined into a new dataset by adding the data columns from the CSV to the geometry data in the Shape file. We have also included a CSVT file which defines the format of the corresponding CSV columns.  This will ensure the CSV columns are imported with the correct data types. For more information on this see our CSV help page.

1.3.  Import data onto your map

Open your new map and import the zip file.  Follow these steps to complete this process:

1.  Click EDIT MAP CONFIG on the toolbar

2.  Choose the DATA tab and click CREATE LAYER

3.  This will exit the map edit screen and redirect you to layer creation.  Click YES, GO!

4.  Create your layer as usual and import it onto the map.

2.    Join your data

2.1.  Using the 'Join Data' tool

Select the ANALYSIS button on the toolbar.

Select the JOIN DATA button and NEXT.

Our 'Join Data' tool will display as this when first selected.  This tool has a few sections which we will explain in turn.

Initially you must choose two layers on the map to join. Select "UScounties" as layer 1 and "US 2016 County Level Presidential Results" as layer 2.

Available join types are as above. See our join data options help page for full explanations of each. For this dataset join we recommend LEFT JOIN.

Select the columns in each dataset that have matching data. Columns must have the same data type - the type is displayed in icon format for each attribute. The join column for layer 1 = "fips" and for layer 2 = "combined_fips"

Choose which dataset you would like to keep the geometry from. In this case only the US counties dataset has a geometry so we chose it.

Choose columns to keep for each layer, you must choose at least one from each layer.

Add a column suffix to the second joined layer.

Set the preview size, choices are 10, 100, 500. Default is 100 records.

The fully ready to join tool should look something like the above.  Click JOIN and wait a few seconds for results preview

2.2.  Preview joined data

If the join is successful you will get the above message with the total joined results.

2.3.  Save your new layer

The preview data will display in data panel. At this point the join is purely temporary. To save the joined data click the SAVE AS A NEW LAYER button, at the top of the data panel. 

Choose a name for your new layer.

Click SAVE. Your new layer will be imported and the map will refresh.

3.    Style your new layer (optional)

Style your layer to make the most of the newly joined data. We styled a thematic map using the "per point diff joined" column resulting in the following map.

For advice on how to create a choropleth map please see our guide.

That's it - Your data is joined.

If you haven't signed up yet go to the Azimap website and click REGISTER.

Enjoy joining your data in the future and thanks for reading the guide.