Preston was surveyed in 1685 and its streets and property frontages carefully delineated. The survey provided considerable information about the townscape at that time. What it did not provide was any information about the fields, moor and marsh occupying the wide area of the town between its urban core and its borough boundaries. This gap was filled by a plan of 1774 on which the fields are numbered and named. In addition there is a survey or index to the plan which relates those numbers to the owners of the land, together with the acreage of each plot and its value.
Plan and survey have been attributed to the Leyland land surveyor George Lang. The 1685 survey was casually, and almost certainly wrongly, attributed to the Preston antiquarian Richard Kuerden on the basis of no reasonable evidence. There is a stronger case for accepting the Lang attribution, but one source attributes the survey to both Lang and Porter (presumably Robert, an 18th-century local surveyor).
The first reference to the Lang plan by Preston historians is found in Hardwick’s history of the town in 1857 in which he relates that, ‘A map of the township of Preston was executed by George Lang, a local surveyor of some repute, in 1774. It is at present in the possession of Mr Philip Park, treasurer to the corporation.’ He includes a copy of the central part of the plan.  The next reference comes in Hewitson’s history of the town of 1883, where a central portion of the plan is again reproduced and again described as being by George Lang. 
Clemesha in an article on the town’s history in 1902 lamented the loss of the plan:
In a lecture given three years ago in Preston by Professor Maitland, the lecturer urged that some effort should be made to discover its town ﬁelds, and pointed out their importance in the history of a town. The materials for their reconstruction are very slight indeed. The earliest map that shows the names of the ﬁelds is Lang’s map of 1774. This map, which has recently been lost, is only known to us now by the reproductions of parts of it which appear in Hardwick’s and Hewitson’s histories, and these reproductions, unfortunately, do not cover the whole of the borough. 
A copy of the plan was discovered by the Preston solicitor A. T. Houghton in his offices, some time before 1923, which he presented to the corporation. In 1923 Houghton discovered a copy of the survey. Clemesha reported these discoveries in an article in the Preston Guardian of 9 June 1923. A copy of this article together with a letter Clemesha wrote to the Preston town clerk requesting that the survey should be kept in the corporation muniment room. 
Clemesha notes that on the cover of the survey is the name of William Carr who he says was a Preston attorney from whom Mr Houghton’s firm traced its descent. If he is the William Carr who appears as a witness on a number of late 18th-century legal documents deposited at Lancashire Archives by Houghton, Craven solicitors then this copy of the survey was probably produced at the same.
At present three copies of the plan appear to have survived. Lancashire Archives has a copy found among the Earl of Derby’s papers together with tracing of the plan, which the archivists date to around 1910.  There is also a photocopy of the plan in the map drawers at the Harris reference library, Preston. This does not seem to be catalogued: could it be the one Houghton deposited with the corporation? This copy differs from the one at the archives: it is in a different hand and the crease marks are different so that an area that is obliterated on the archives copy is clear on the Harris copy. None of these copies of the survey or plan carries the name of a creator. There are four copies of the survey at Lancashire Archives (DDK1549/1-4) and a copy at the Harris reference library. 
There is another document among the Derby papers filed with the survey and plan, bearing the title ‘Survey of Lord Derby’s old Estate in Preston 1774’. Inside it is stated to be a ‘Copy of Survey by Messrs Lang & Porter 1774 far as concerns the Rt Hon Lord Derby Property in Preston’. This is the only original document naming the surveyors, all other references are in secondary sources, and they only mention Lang.  The second surveyor would most likely be Robert Porter of Goosnargh. There is some doubt about the 1774 dating of this document. It is split into two sections, one for land (which details five holdings from the full survey) and one for buildings: the buildings are not mentioned in the full survey.
Four of the holdings are described thus in this copy: late Walshman’s Heirs (Water Willow and Nearer Water Willow); late Farrers (Toad Croft); late Lutwidge (Brick Kiln Field and Mary Hey, with the note ‘Now in one’); and late Lorrimer’s (Barn, Barn Field & Barn, New Hall Lane Field, Great Far Field and Little Far Field).
In the full survey Mr Walshman’s heirs are still in possession, as is Mr Robert Farrer, as is Henry Lutwidge esq and as is Mr Thomas Lorimer; on the plan Brick Kiln Field and Mary (or Marled) Hey have not been combined; and most of the land values in the Derby document are double those in the full survey of 1774. This suggests the date 1774 in the Derby survey was referencing the original 1774 survey and was itself produced later, after the various property transactions had taken place.
In fact, William Farrer, possibly Robert’s son, did not sell the lease to Toad Croft to the Earl of Derby until 1786.  And it was not until 1785 that Henry Lutwidge began selling his land in Preston to the Earl of Derby.  The Brick Field (or Brick Kiln Field) transaction is recorded in 1787.  These transactions cast doubt on dating the Derby document (DDK1549/5) to 1774, rather suggesting a date after 1787.
Another complicating factor is that both plan and survey specify the Lancashire long acre of seven yards to the pole as the measurement used, rather than the statute 16 and a half feet. This leads Clemesha astray in his discussion of the size of individual holdings for he treats the measure as statute.
The above figure shows the first page of the survey with the total land holding for Garlick’s heirs given as 21 acres, 2 roods and 17 perches, whereas the figures given actually add up to 21 acres, 0 roods and 37 perches. There are other small errors in the additions elsewhere in the survey, but not such as to make a significant difference to the figures. Any discrepancies will be pointed out in discussions of individual land holdings.
Another anomaly in the survey is that is some cases the annual value of the plot is given, but the value per acre is omitted, yet the omitted value must have been known in order to calculate the annual value. For analysis purposes, in these cases the value per acre has been calculated by dividing the annual value by the acreage of the plot. In other cases no value per acre is given and two or more plots are bracketed together to give a total annual value. In these cases, which are few and involve only small plots, the resulting calculation assigned per plot is an average of the values of the plots bracketed together. The impact of these steps on the overall analysis of land values is minimal.
There are also plots on the plan that do not appear in the survey. For example, in the figure above Lord Stanley’s Garden is clearly shown to the rear of Patten House on the north side of Church Street with an area of 1 acre, 1 rood and 3 perches (slightly over two statute acres). It is not in the survey. A one-acre plot named Whittaker Gardens is listed in the survey but does not appear on the plan.
Allowing for these discrepancies it can be said that the total area of cultivated land in 1774 was roughly 1,600 statute acres; to add to this would be the many small cultivated plots within the urban core and the building plots, none of which features in the survey. There were also roughly 270 acres of moorland (Preston Moor) and roughly 40 acres of marsh (Preston Marsh).
The purpose of the survey is not stated on the documents. The survey groups the fields by owner and assigns a value to each plot, totalling both the holding and the value for individual owners. This suggests that it was prepared for taxation purposes, possibly for the corporation. The plan has the inscription ‘Buildings belonging to the Corporation’ in the bottom right corner. There was possibly a coloured original on which these buildings could be distinguished. Several plots in the survey are labelled ‘Corporation Land’: here the people listed against the plots are probably lessees, not owners.
The maps below demonstrates how extensively the landscape had been covered in houses and factories just 75 years after the completion of the 1774 survey. The landscape at the time of the survey had changed little since medieval times.