The western limit of the settlement is marked by the valley of the Sills Burn, which flows into the Rede just above Rochester village. To the north lies a vast expanse of high barren moorland, incorporated in the Otterburn Training Area. During the 17th and 19th centuries Rochester was the centre of the large Poor Law Township or 'ward' of Rochester. However this area, which extended from Rochester right up to the head of the valley and the border with Scotland at Carter Bar (excluding only extra-parochial Ramshope), was too large to use as the basis of this study.
Accordingly, a much smaller study area has been adopted which is focussed on Rochester village. This embraces the pre-1662 territorial township which is still depicted on tithe, enclosure and estate maps of the 18th and 19th centuries. It covers both High and Low Rochester and the surrounding farmsteads of Hillock, Dykehead and Petty Knowes, and is bounded by the Rede to the south and the Sills Burn to the west.