Are continuous variables for detection and categorical for density estimations?

Question

This is probably a very basic yes or no question, I’m not very clued up with statistical analysis and R. I am doing a distance sampling analysis using unmarked. For the function distsamp(~1~1, umf) , I understand that the first ~1 should be a detection covariates and the second ~1 should be a density covariate. Am I correct to think that categorical variables are for density, whilst continuous or discrete variables are for detection?