Recap: Vector Data Model

• Each discrete object is considered to be a feature
• Vector features have attributes, which consist of text or numerical information that describe the features
• A vector feature has its shape represented using geometry
• The geometry is made up of one or more interconnected vertices

Features and Attributes

• Each Feature has a corresponding Record or Row in the Attribute Table
• The ordering of these rows has no intrinsic meaning
• Each Feature has a unique ID this is relied upon to link the row to the feature

Example Data

• Voting Precincts: Riverside County 2016
• [Download]
• [Source]

Voting Precincts: Riverside County 2016

Attribute Table

Table Joins

Loading csv layer

Sort two tables by their precinct attribute

Table Join

• We want to attach the data from the csv table into the shapefile layer
• While the two precinct attributes are aligned, they have different values pointing to the same precinct
• We need to fix this prior to doing a table join

Creating New Attributes

• We will first create a new attribute in the csv layer that has values matching those in the relevant field in the shapefile layer.
• To do so we will make use of the Field Calculator of attribute tables
• We are going to proceed in several steps
• Ultimately we want to create a new field that changes 065-11103 into 11-103

Create an Interim Field

Create the Final New Field

New Field in Attribute Table

Table Join

• Now were in a position to do a table join
• In the shapefile layer, open its properties dialog and select Joins

Table Join

• Ensure your dialog has the values as in the previous image
• Then click apply
• Open up the attribute table for the layer

Save our layer as a new name

It is good practice to save layers that have changed to a new layer.

This ensures the values for the fields are updated.

Save your layer as voting joined

Munged Field Names

One issue is our field names got changed when we saved to a new layers

Fixing Field Names

We can fix this:

• open the layer properties dialog and select Source Fields

Turn on field editing by clicking the pencil icon

• Edit the name for the relevant field

Turn editing off by clicking the pencil

Creating More Attributes

• We will limit our attention to the 2016 presidential results
• Let’s create a few new attributes that help us study these results

Create a new variable that is the total of Clinton + Trump

New Total

Create a pctClinton Attribute

New pctClinton Attribute

Create a Winner Attribute (String)

New Winner Attribute (String)

Symbology

Sybmology Default

Sybmology Changing Fill Colors

Virtual Layers

Virtual Layer Menu

Getting the path

Path set

Query

Test Query

Accessing Virtual Layer Attribute Tables

Query Result

Rename Virtual Layer

• right click on the virtual layer
• click rename
• rename to clinton_trump_total

Duplicate Layer

Rename Duplicate Layer

Edit New Virtual Layer

Query for Tracts Won by Candidate

Warning

Result: Tracts Won by Candidate

Next Up

• Raster Data