In many instances boundaries had to be defined in exact terms with land being assigned to a specific parish. The variation in tithe payments between parishes meant that boundary decisions were often hotly disputed by both tithe owners and tithe payers, for land subject to tithe on one side of a boundary may have been exempt on the other. Once the districts had been established, the next step was to determine the total value of tithes payable within them. This was done by examining the previous seven years of receipts by the tithe owners. The tithe Act allowed for the involved parties to reach a provisional agreement before 1 October 1838. If an agreement was not forthcoming then the Commissioners were empowered to impose an evaluation which was binding on all parties.

When a overall value for the tithe in a district or parish had been determined, the corn rent charge had to be apportioned among the lands of that parish. The figure for Swansea Parish was £424 which had to be apportioned fairly throughout the lands of the parish. For example, within Swansea parish the farm of Penlan consisted of eight fields with a total area of twenty-two acres, three roods, and thirty perches. The tithe payment of the farm was calculated at thirteen shillings. The larger farm of Caergynydd Fawr with thirty-six enclosures and a total size of one hundred and sixty-one acres, two roods, and thirty-seven perches was valued at £6. In this way each unit of land was valued as a fraction of the £424 of the whole parish.

It proved to be an extremely difficult task to apportion the rent charge equitably among lands of differing quality and various uses. The farmlands of Sketty were valued more highly than those of Cockett or Gors. In the past, farmers had been able to reduce the amount of tithes payable by converting arable land to meadow or pasture and thereby substituting a mixed tithe for a predial tithe of corn or hay. At first the Commissioners did attempt to evaluate the potential of a piece of land for improved yields or the deliberate attempts by farmers to change land use and reduce their payments, but in the end this proved too difficult and time consuming. In practice, lands were evaluated on their observed state of cultivation at the time of their inspection.

In order to determine boundaries of land, acreage of fields, and states of cultivation, an extremely detailed survey of the landscape was needed. In 1835 there were no Ordnance Survey maps at a scale large enough for the purpose, so the Commissioners arranged for their own surveys to be undertaken. In November 1836 Tithe Commission surveyors were issued with detailed instructions on the nature of the surveys. The priorities being to give an accurate measurement of acreage and record of the state of cultivation; lands were to be classified as arable, grass, meadow, pasture, common, wood, plantation, orchard, hop ground or market garden. Local variations often required skilled interpretation of the instructions. In general, the most important distinction was between arable land and permanent grassland. Between 1836 and 1851, over eleven thousand districts were surveyed. It was noticeable that most of the survey work was completed in a tenth of the time taken by the Ordnance Survey to complete its 1:2500 scale plans of the same areas some years later. Yet, as some historians have noted, speed was achieved without sacrificing accuracy.