What's the difference between the Location and Fitter Location columns in the Pin Planner?
Why some Pins have assignments in the Fitter Location column but do not have assignments in the Location column?
After you run the 'Analysis & Synthesis, the compiler will help to auto assign the pin assignment as user no define the location. You can also to change it by yourself. There is some pin location is not assigned due to the component is user defined, thus the compiler is not assign the pin location.
In the column Fitter Location shows which pin the autofitter function has selected - but it is usually possible to make other choices yourself.