Every project has assumptions. How much does it cost to build? What is the monthly rent? What is the building efficiency? How much parking is required? Usages are where you manage assumptions about your project.
A Usage is an urban typology you apply to a shape in Giraffe that bundles up a set of property values (like cost, unit mix, parking needs, etc.). Those assumptions then feed into calculations, so your drawn geometry can be turned into useful reports and insights.
So instead of setting those values on every single shape, you set them once on the usage, and anything using that usage inherits them.
Before you get started, review all of the assumptions in your usages to make sure they reflect your company's secret sauce.