Churton Park doesn’t have a lot of variety of Pokemon available to catch. Mostly Zubats, Weedles, Caterpies, Eevees and Clefairys with the odd Paras, Nidoran, Venonat, Oddish and occasionally a Bellsprout thrown in. However, I’ve noticed that all the rare Pokemon I’ve caught in Churton Park seem to have spawned in one location. Specifically on Halswater Drive, half way from the T junction to the sports field. From this same spawn spot, I’ve got a Geodude, Gravler, Gastly and today a Muk!
It is therefore my theory that Pokemon Go has rare spawn locations that are definied.