  We analyse the capacity of several two-dimensional constraint families - the
exclusion, colouring, parity and charge model families. Using Baxter's corner
transfer matrix formalism combined with the corner transfer matrix
renormalisation group method of Nishino and Okunishi, we calculate very tight
lower bounds and estimates on the growth rate of these models. Our results
strongly improve previous known lower bounds, and lead to the surprising
conjecture that the capacity of the even and charge(3) constraints are
identical.
