PUBLIC RECORD OFFICE
Reference —
FEC.O. 885
ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH-NOT TO
20 PUBLIC RECORD OFFICE, LONDON
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The positions of the fixed points throughout the country are permanently recorded in three places: (a) in the field books; (b) on the computation forms; (c) on the manuscript plotted sheets. All these are kept in one building in Lagos, so that there is a possibility, not, perhaps, a serious one, of the destruction of the whole by fire. As this would cause grave loss, the co-ordinates of all these points should be extracted into a ledger deposited elsewhere than in the survey office. The elerical work involved would be trifling.
The precision of the main traverse lines is probably much in excess of that laid No down as necessary in the Secretary of State's instructions of March, 1908. minor traverses of the class contemplated in those instructions have been run. After computation, the traverses are plotted by co-ordinates upon a large scale, and the plot is then reduced by eidograph to 125000. This is not a good practice; The use of a plotting they should be plotted direct upon the scale of the map. machine, such as the co-ordinatograph, made by Coradi, of Zurich, found of such great value upon the cadastral survey of Egypt, would result in a large saving in The standardisation of the tapes time with a corresponding gain in precision. requires attention. At present the only standard used is a five-chain steel band, the private property of Mr. Cotton, brought by him from Brisbane in 1901. There is also an old Ordnance Survey standard brass chain which has not been used lately, nor are there any records of its constants. An enquiry has recently been made by the Director-General of the Ordnance Surveys (in a letter, dated 3rd March, 1909) as to the general question of the standards of length in the Protectorate, and an offer has been made to compare a bar or tape with the standards at Southampton. Advantage should be taken of this offer, but when money is available a standard invar wire should be purchased and a ground comparison standard laid down in the Survey Office compound at Lagos.
(3) Compass Traverses.—' These are executed with 4-inch compasses and steel tapes. They are of an unnecessary degree of accuracy, and the rate at which they are done does not exceed the average for first-class theodolite work, about 5-6 miles per day.
With a rougher means of distance measurement, say, a wheel with cyclo- meter, all the requisite accuracy could be attained and nearly double the distance accomplished daily.
The plotting is done on a large scale by protractor and reduced by eidograph. This is a correct procedure so long as the compass traverses are plotted in the central office and so long as the compass details and the contouring are done by different men at different times. This arrangement of work is, however, a cumbrous one, and it would be more satisfactory for one man to carry out the detail and contour survey simultaneously. In this case, the surveyor would himself plot his compass traverses direct on his plane-table sheets.
(4) Levels and Contouring.-No instrumental levelling has been done except a line from Lagos to Iju along the railway (16 miles), in connection with the water- supply scheme. Beyond that point the railway levels have been taken as the data. These are, presumably, correct within a few feet, but it is not safe to take them as final. This was clearly implied in the Secretary of State's instructions, wherein it No work of this was also laid down that certain minor level lines should be run. character has been begun or even planned.
Away from the railway the vertical framework of the map depends upon differ- ences of height determined by simultaneous readings of mercurial barometers connected by lines run by aneroids.
The contouring is rough and incomplete. The present practice is to give a surveyor an area of 15 minutes square. A copy of the plotted skeleton sheet is prepared by photography. This copy, which is taken into the field, is intended to A photo. be used as a plane-table sheet, on which the contours are to be inserted. reproduction is, however, not very suitable for use on a plane table, especially in a damp tropical climate, and, as a matter of fact, the plane table is little used, and none of the men have been taught the orthodox methods of contouring, Little or no instruction is given to the surveyors as to the methods of survey they are to employ, and no definite orders are issued as to the form in which the work is to be sent in. Some of the men send theirs in upon the photo. sheets in pencil, some draw it out fair upon tracing cloth, and some merely send in their field books, leaving the results to be puzzled out in the Headquarter Office.
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The contourer is expected to include any detail he comes across, part of the detail having been already inserted by the compass traverser. There is thus no one man responsible for the detail in a given area; no field examination of the finished sheet is made by a superior officer, and no check exists upon the accuracy or com- pleteness of each surveyor's work. The contours are inserted at 50-feet vertical intervals, instead of the 100-feet proper to the scale; they are seldom followed away from the roads, and the whole map is a crude and unprofessional production.
It is doubtful whether any portion of the existing contour survey is worth publication.
For the immediate future, it is essential that a system of vertical heights should Le established with the least possible delay. On the assumption that the triangula- tion is started in the interior, the best procedure would appear to be to carry a line of levels up the railway as far as Aro, and thence fix the height of one of the promi- nent rocky hills in that neighbourhood. The triangulation can be rapidly extended to include this point, and the datum will thus be fixed at a much earlier date than if it is made to depend upon the triangulation reaching the coast. Owing to the dense forest belt to be traversed, this latter may take some time..
(5) Cadastral Surveys.-These are executed chiefly for legal, Land Office, rail- way, and public works purposes, and are mostly in Lagos and vicinity.
The method of survey is the standard one, traverses with 6-inch theodolites and steel tapes, and the trained native members of the staff appear to be competent to execute the work. With the exception of the system of computing and drafting, the defects of which have been already alluded to, and the fact that field books are kept in pencil, no particular criticisms arise. It must, however, be noted that no attention has been paid to the orders that cadastral surveys should be on natural scales, 301000, or 2500; at present all sorts of scales are used, generally in so many links to the inch.
The Director claims that the survey exercises the greatest care to leave proper mark-stones in the ground. This optimism is not shared by other Government Departments; on the contrary, it is reported that the survey is most careless in this matter, and that independent verification of any ground-marks shown on a plan is both habitual and necessary.
The existing cadastral map of Lagos was executed by an Ordnance Survey party, under Captain Buckland, R.E., in 1892. The Director has worked upon the assumption that it is not possible to keep this map revised to date, and claims that the Ordnance Survey left no permanent marks on the ground. He has, how- ever, taken no steps to ascertain direct from Southampton whether this is really
the case.
A
map revised to date is urgently called for, and it is imperative that it should be taken in hand energetically. Much, if not all, of the necessary work might be done by the Instructor in the Survey School with selected parties of second or third year pupils. The first obvious step to be taken is to plot all the scattered surveys that have been done throughout the island on to general cadastral sheets.
Survey School.
The Survey School for the training of natives has been in existence nearly a year, and its condition exhibits clearly the want of initiative and organising power of the present Director of Surveys.
It is unfortunate that the School has been inaugurated without the European Instructor. The native Instructor (Mr. Barnes) appears to be a competent man. but it is futile to expect that a native can be trusted to organise an entirely new machine without any adequate direction or guidance.
The methods are quite haphazard. No time table has been drawn up, no definite courses of instruction have been laid down, no text-books have been adopted, no fixed terms and vacations have been settled. The present seven boys have now been working for eleven months without any holidays. The authorised schedule of instruction is not adhered to; for example, the pupils have recently spent two months in the field doing practical surveying, a course clearly not contemplated in the first year's instruction.
The boys appear to come to the School with a good general education, and while they have doubtless learned something during the year, it is impossible to say how much. Their progress is ostensibly tested by periodical examinations. As, how- ever, the questions in these examinations are set by the Instructor, he alone is
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