“To normalize, in a statistical sense, is to transform a set of measurements so that they may be compared in a meaningful way. Technically, normalization involves factoring out the size of the domain when you wish to compare counts collected over unequal areas or populations. Normalization transforms measures of magnitude (counts or weights) into measures of intensity.”
This tutorial will cover how to turn counts into percents in QGIS.
Download the sample data, tenure by census tract in Cambridge, MA.
Right click the tenure data layer in the layer list and select
Open Attribute Table.
Scroll all the way to the right to find the three census variables we will be working with. Note their names, something along the lines of
tenure-2019_SE_A10060_003. From the codebook which came along with the download we know that these fields are the total number of housing units, the number (or count) of owner-occupied units, and the number of renter-occupied units. We need to use these fields to create new percent fields.
Select the menu icon that looks like an abacus called
Open field calculator.
Create a new field is checked on.
Output field name, name the field
Output field type, select
Decimal number (real).
("tenure-2019_SE_A10060_002" / "tenure-2019_SE_A10060_001") * 100.
You will know your expression is valid if under the expression box there is an
Output previewwith a value that looks like a valid percentage.
OK and scroll to the right of the attribute table to ensure your new field has populated.
Repeat steps 3-8 for the renter occupied variable.