I was an EHO enforcing conditions on food vans for many years and I found that vans would move to different sites at different times of day eg outside schools at lunch breaks and outside discos at night. As long as they were licensed within our area ( admittedly a very small area) this was not a problem but I did feel that other factors had an influence on where people traded. It was almost as if there was some sort of unwritten traders' agreement.