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PART THE SEVENTH.

THE METHOD OF MEASURING AND PLANNING VILLAGES, TOWNS, AND CITIES; DIRECTIONS FOR MEASURING AND PLANNING BUILDING GROUND, AND DIVIDING IT INTO CONVENIENT LOTS FOR SALE; AND MISCELLANEOUS QUESTIONS RELATING TO SURVEYING, LAYING-OUT, PARTING-OFF, AND DIVIDING LAND.

SECTION I.

The Method of measuring and planning Villages, Towns, and

Cities.

As villages, towns, or cities, present themselves in almost every extensive survey, and are generally measured and planned with the adjoining or surrounding lands, it is highly necessary that something should be said on the method of taking and laying down the dimensions of such places, and finishing the plans.

Besides, the plans of towns and cities are so essentially necessary for the purposes of commercial and general reference, that Surveyors are not unfrequently employed in forming correct drawings of the same, in order to have them engraved and published in copperplates.

Without this art, we could not obtain the ichnography of towns and cities; neither could we have any just idea of the shape, extent, and direction of the streets; the size and number of the public buildings; the local conveniences enjoyed by the inhabitants, &c. &c. of those places which circumstances will not permit us to visit.

Directions for taking the Dimensions of Villages, Towns, and Cities.

The dimensions of villages, towns, and cities, may generally be obtained by the chain only; as the streets are usually wide enough to admit of angles or tie-lines being taken with the chain, at the meetings or intersections of the streets, in the same manner as directed in Problems 4 and 5, Part IV. In these Problems the methods of measuring meres, woods, roads, rivers, and canals, are clearly illus

trated and exemplified; and if the learner make himself completely master of those departments of Surveying, any difficulties which may present themselves in measuring villages, towns, or cities, will be easily surmounted.

It will sometimes happen that the tie-lines cannot be measured at a greater distance from the angular points than 30 or 40 links. In such cases, the tie-lines must be taken to a quarter of a link, and both them and the angular distances must be multiplied by 2, 3, 4, or any larger number, as circumstances may require; and the products used in laying down the chain-lines. (See Prob. II. Part IV.)

The notes taken in measuring towns and cities must be entered precisely in the same manner as in surveying estates; and in measuring along the streets, offsets must be taken to the houses on both sides of the chain-line; and particularly to every corner and projection; even the small projections of bow-windows must not be omitted.

Sketches of the bases of the buildings, particularly the corners and projections, must be made in the margin of the note-book, in order to assist the Surveyor in drawing a correct plan.

All public buildings, such as churches, prisons, castles, court-houses, market-places, halls, colleges, mansion-houses, &c. &c. must be distinctly noticed; and the range of the first line should be taken with the compass, in order that the Draftsman may be able to lay down every street in its true direction.

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NOTE 1. - In measuring along the streets, all the offsets to the buildings must be taken at right-angles to the chain lines. The bases of the buildings, and all the projections must be sketched, as you proceed; and the breadths of the buildings, the lengths and breadths of the projections, &c. &c. must be correctly measured and entered opposite to those parts of the sketch to which they respectively belong. The sign + (plus) is usually placed between the breadth of a building, at its perpendicular distance from the chain-line. The method of sketching the bases of buildings, and entering the notes, is exemplified in pages 4, 10, and 12, of the engraven Field-book, to which the Learner is referred. (See Plate VII. No. 7, Page 199.)

2. When a town and the surrounding or adjoining lands are both to be measured and planned together, the dimensions must be taken with Gunter's chain; and the lines measured along the streets must be properly connected with those measured in surveying the adjoining estates; but if the plan of a town only is required, it is more convenient to take the dimensions with a chain of 50 feet in length, divided into 50 links, and an offset-staff of 10 feet in length.

3. As station staves cannot be fixed in the streets, in consequence of the pavement, they must either be set in wooden pedestals, made for that purpose, or two or more assistants must each hold a staff in these places that are pointed out by the Surveyor.

4. Sometimes it is most convenient to measure external or main-lines, on the outside of the town, as in Surveying a mere or wood, Prob. IV. Part IV.; and in running such lines, stations must be left at the ends of the streets, as you pass

them, in order that lines may be run from one station to another in measuring the

streets.

5. In some situations, and under certain circumstances, it is more eligible to measure the first line along one of the principal streets; and to intersect this line by another, measured along some other principal street, nearly at right-angles with the former; then these two lines being tied together by a connecting line, measured in the most convenient manner, will divide the town into four parts, each of which may be measured separately, by running lines in the most advantageous manner. (See a similar Remark in Note 5, Method I. Part V.)

6. In putting down stations at the ends of the streets, &c. the number of the station may be made upon the wall of the opposite building (if there be one) with red or white chalk, in such a situation that an offset may be taken, at rightangles to the building, from the station marked upon the wall, to the station on the chain-line. This offset being entered in the book, and again measured from the station on the wall, at right-angles to the building, will give you the station on the chain-line, whenever you may want to find it.

7. When the foregoing method cannot be adopted in consequence of not being able to take a right-angled offset from any building to the station which you wish to fix, then two lines may be measured from the station to the corners, or to any other parts of two adjoining buildings; and the intersection of these lines, when measured from the buildings, will give the station required.

8. After all the principal streets have been measured, then proceed to the smaller and intermediate streets; and lastly to the lanes, alleys, courts, yards, and every other part which it may be thought necessary to represent upon the plan.

9. When any of the streets are so narrow as not to admit of tie-lines being taken with the chain, the angles which the chain-lines make with each other, at the meetings or intersections of the streets, must be taken in degrees and minutes, by a theodolite; and in planning, they must be laid down as directed in Problems 20 and 21, Part I. (See the Description of the Theodolite, Page 291.)

10. What has been advanced on this subject will, no doubt, be acceptable to Learners; but as towns are built after such a variety of plans, and consequently vary so much in their forms, no directions can be given that will be applicable to every particular case to be met with in practice. A great deal will always depend upon the skill and judgment of the Surveyor, who should, after duly examining every part of the town, endeavour to run his lines in the most advantageous manner.

EXAMPLE.

Let it be required to measure the New Town, No. 7, Plate VII. In order to follow the method described in Note 4, we shall begin at the south-west corner, as in Problem 4, Part IV.; although the survey would be conducted precisely in the same manner, if we began any other corner.

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First Line. Put down + 1, at the S. W. corner, and proceed towards the S. E. corner; taking offsets to the buildings, wherever it is necessary; and sketching their bases in the margin of the notebook. At the end of High Street, put down + 2; at Queen Street,

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+3; at Low Street, + 4; at the S. E. corner, + 5; and produce the line at pleasure, to + 6.

Second Line. From +5, proceed towards the N. E. corner; but when you arrive at the end of York Street, put down +7; and thence run a tie-line to +6. From +7, proceed with the main-line; and at King Street, put down + 8; at George Street, + 9; at the N. E. corner, 10; and continue the line to + 11.

Third Line. From + 10, go towards the N. W. corner; but when you come to the end of Low Street, put down + 12, from which run a tie-line to + 11. Proceed from + 12; and at the end of Queen Street, put down + 13; at High Street, + 14; and at the N. W. corner, +15.

Fourth Line.

From +15, proceed towards the S. W. corner; and at the end of George Street, put down + 16; at King Street,+ 17; at York Street, + 18; and continuing the line to + 1, you will have circumscribed the town with four main-lines, into which the lines measured along the streets must be run.

NOTE. After the first three lines are laid down, it is evident that the fourth line will serve as a check; and will reach exactly from + 15 to + 1, if all the operations have been conducted with accuracy.

Fifth Line.

From + 18, through York Street, to +7.

Sixth Line.

From + 8, along King Street, to + 17.

Seventh Line.

Eighth Line.

From + 16, through George Street, to + 9.
From + 12, along Low Street, to + 4.

Ninth Line. From + 3, through Queen Street, to + 13.

Tenth Line. From + 14, along High Street, to + 2; thus the survey of the town is completed.

NOTE 1. The chain-lines and stations do not appear upon the plan, as they could not have been conveniently entered without increasing its size; the learner will, however, find no difficulty in making a similar plan, two or three times as large; drawing the chain-lines, and putting down the stations in their proper places. Or he may take the dimensions of the given plan with a small scale; enter them in a note-book; and then draw a rough plan by a larger scale, and after that a finished one, which will be an exercise that will tend much to his improvement. 2. The survey of this town might have been carried on according to the directions given in Note 5, by measuring a line through King Street, and another through Queen Street; and then connecting these two lines together by tie-lines taken at the point of intersection. Thus would the town be divided into four parts, each of which might be measured separately.

3. Here it will be proper to observe, that in taking an angle with the chain or theodolite, at the intersection or meeting of two lines, either the external or internal angle may be taken, as circumstances may make it most convenient; but it should always be remembered, that neither very acute, nor very obtuse angles should be measured, if it can be avoided, as both are liable to errors, in laying down. Those angles which approach nearest to right-angles should always be preferred, as being most correct.

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4. By way of proof, it is an excellent plan to take both the angles. taken by the chain, you will have a check-line, by the scale; and if taken by the theodolite, their sum should be 180 degrees; and you will also have a proof in planning, in consequence of having measured an angle and its supplement. (See Definition 16, and Problems 20 and 21, Part I.)

A Description of the Theodolite.

The theodolite is a mathematical instrument used by Surveyors, for taking horizontal angles, in measuring meres, woods, roads, rivers, canals, villages, towns, cities, &c. &c. when tie-lines cannot be taken by the chain, in consequence of obstructions. It also enables us to take such angles as are necessary for calculating the heights and distances of remote objects by plane trigonometry.

There are various forms of this instrument, arising from the successive improvements of many eminent artists; but the principle of its operation is the same in all, whatever difference may appear in the construction.

A theodolite of the best kind consists of the following principal parts:

1. A telescope to direct the sight, and enable the operator to distinguish objects at a distance. To the telescope is attached a spiritlevel, to assist the operator in placing the instrument in a horizontal position.

2. A vertical arc for taking angles of altitude and depression.

One side of this arc is graduated to every half degree; and these are again subdivided to every minute of a degree by the index or nonius. This side is numbered from 0 to 90 degrees, towards the eye-end, for angles of altitude; and from 0 to 50 degrees, towards the object-end, for angles of depression.

The other side of the vertical arc contains a line of divisions, showing the number of links to be deducted from each chain's length, in measuring up or down any ascent or descent, in order to reduce it to a true horizontal line, according to the directions given for surveying hilly ground, Method I, Part IV.

3. A horizontal limb and compass, for taking horizontal angles, and the bearings of objects.

The horizontal limb consists of two circular plates, one movable on the other; and the outer edge of the upper plate contains an index to the degrees and minutes on the lower plate. The upper plate, together with the compass, vertical arc, telescope, and level, are easily turned round upon a centre.

The lower plate of the horizontal limb is divided to half degrees;

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