A Join operation is a process that links information contained in one attribute table to another, by using a common ID field. The goal of this tutorial is to become familiar with how to Join a Data Source with a table that comes from a CSV file.
1) Download the dataset required to complete this exercise. You will find among others a Shapefiles of Intersections (intersection.zip). Import this file into eVouala and name it Intersections.
Note: The data are from the Guelph city open data website.
2) Also, import the CSV file IntersectionVolume.csv and name it IntersectionVolume.
3) Open the Process page. You can create processes from the Library using the Process option with the Add to Library... button, or through the main menu by using the "+" button.
4) Observe the three sections of this page. The leftmost section contains the available fields creator option (also called operators), the middle section contains the chain of operators of the treatment while the rightmost section represents an overview of the result of the process.
5) Choose the initial Data Source by clicking the Browse ... button and select the Intersections Data source.
6) To Join another Data Source to this one, click on the Join operator and drag and drop it in the center section, under the initial Data source.
7) You will notice that an operator needs a Data Source to work properly. Click the Browse ... button and select your CSV file named IntersectionVolume.
8) You now have to select the fields to Join. The first field to select comes from Point Data source (Intersections) and the second field comes from the imported CSV Data source (IntersectionVolume). Use the common geoid field. The last option of the Join operator is the join type (Inner Join is the default)
9) Run the process by clicking on the play button at the bottom of the page. Observe the changes in the table on the right. You can now see the column with the traffic volume at intersections.
10) Save your process by clicking the Save or Save and Close buttons. You now have a Data Source from your process. Go back to your Library and notice the difference between the icons of the normal Data Sources and those of a process. Et vouala!