The Join is a process that links information contained in one attribute table to another. To do this, the two tables to be joined must have common fields. CSV (comma-separated values) tabular files are extremely popular as a data exchange format. This type of file is very often the preferred format on Open data web sites. It is also be very easy to export a Microsoft Excel (XLS or XLSX) or Libre Office (ODS) file in CSV format.
The goal of this tutorial is to become familiar with how to Join a Data Source with a table that comes from from a CSV tabular file. To do this, we will use open data from the City of Guelph.
1) Download the dataset (http://dl.mapgears.com/guelph_datapack.zip) required to complete this exercice. You will find among others the Shapefiles of Intersections. 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. 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 anywhere in the Platform using the + menu. Observe the three sections of this page. The leftmost section contains the available processes (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.
4) You can now choose the initial Data Source. Click the Browse ... button and select the Intersections layer.
5) Choose the process you want to do. In this case, click on the Join operator and drag and drop it in the center section, under the initial layer.
6) You will notice that an operator needs a Data Source to work properly. Click the Browse ... button and select your CSV file named IntersectionVolume.
7) You now have to enter the fields to do the Join. The first field is the geometry field of the process to use for the Join. In this case, use the id field. The second field represents the secondary Data Source to use for the Join. Use the uuid field. The third field is where the Join will appear in the attribute table of the right section. You can choose this option according to your preferences.
8) Run the process by clicking on the 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.
9) 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!