Changing field types so graduated symbols are available

What are graduated symbols in GIS?

Graduated symbols are used to show a quantitative difference between mapped features by varying the size of symbols. Data is classified into ranges that are each then assigned a symbol size to represent the range. For instance, if your classification scheme has four classes, four different symbol sizes are assigned.

How do I use graduated symbology in Qgis?

If you have numeric data you want to symbolize (i.e. total population) choose “Graduated” symbology.

1. Next to the Column option, use the drop-down arrow to select Graduated, and select a field with numerical data.
2. Choose a classification mode, define the number of classes, and click on Classify.