7.1: Topographic Surveys

1. Transit-stadia/theodolite-stadia method 2. Plane table 3. Total stations 4. Photogrammetry 5. Global positioning system.

5 Methods of obtaining topography

Template method

Consists of a series of equally spaced parallel lines that are drawn on transparent film or paper using any specified scale. Series of converging lines may also be graduated and used for interpolating contour lines between plotted elevations.

Approximate contour

Contour accuracy cannot be definitely determined. The area may be inaccesible on the ground or it may be difficult to interpret contours from aerial photographs when heavy cloud or shadow occurs. Map makers has to make an educated guess.

Topography

Defined as the shape, configuration, roughness or three dimensional quality of earth's surface.

Interval

Difference in the values between the lines.

Engineers Planners Foresters Geologist Archeologist Geographers Scientist

Disciplines that applies topography

Depression contour

Drawn to show low spots as excavations around which contour close.

Form line

Drawn when not enough vertical control is available or when the surface is too irregular or intricate contour.

Controlling point method

Elevations are determined for key or controlling points and the contour lines interpolated between them.

Spot heights

Elevations of important features and critical points such as road junctions, peaks, summit sags and highway crossings are indicated in the map

Fifth line

Every _______________ is given a thicker line to make elevation easier to find.

Engineers and planners

Find efficient locations for highways, railroads, canals, pipelines, transmission lines etc.

1. Index contour 2. Intermediate contour​ 3. Depression contour 4. Supplemental/ Auxiliary contour 5. Approximate contour

Five different types if contours

Purpose of the map

For the design of detailed engineering constructions or for the measurements if earthwork quantities, close contouring will be required.

Variable scales.

Has a graduated springs which when stretched, also allows convenient marks to fall on the known Elevation.

Gentle slope

In hachures, the lines are fine and widely spaced

Steep slope

In hachures, the lines are heavy and closely spaced.

Contour lines for hills

Inner loops are higher in elevations with outer loops.

Contour lines for ditches

Inner loops are lower in elevation with outer loops higher.

Feathering

Intermediate contours are so closely spaced as to nearly unite or merge into a single line, it is standard practice for readability not to portray the lines for short distances.

Geologist

Investigate mineral oil, water and other resources.

Hachures

It gives a general impression of the configuration of the ground, they do not provide numerical values such as elevations of tye ground.

Break lines

It marks the bottom or top a hill or ditch

Light detection and ranging

LiDAR

Scale of the map

The contour interval should be in inverse ratio to the scale of the map. If the map scale is reduced, interval must be increased, otherwise lines are crowded.

Checkboard Method

The desired area is divided into squares or rectangles and the elevation determined in the corners of each of these figures.

Intermediate contour

The four lighter weight contours found between the index contours. They conform to the contour interval specified for the map.

Plane table

The measurements were made in the same way as the transit-stadia method, but the data was plotted in the field on paper that was attached to a drawing board mounted on a tripod.

Relief or terrain models.

The model is a representation of the terrain done in three dimensional aspect to suitable horizontal and vertical scales. (Miniature of the terrain)

Subaqueous Contour

The portrayal of the relief of the ground underwater is done by using depth curves or blue lines.

Form lines

Usually represented as dashed lines and do not portray any actual elevations.

1. Location of property 2. Direction of north meridian 3. Available access​ to property. 4. Information concerning property corners and monuments. 5. Sufficient elevations to plot contours. 6. Locations, sizes and descriptions of buildings. 7. Locations and sizes if any roads.

7 Checklist of items to be included on a topographic map.

1. Spot heights 2. Hachures 3. Form line 4. Contour lines or Isohypse 5. Layer tinting system 6. Shading 7. Relief or Terrain Models 8. Ridge and Stream Lining 9. Subaqueous contours

9 different methods in representing relief

Nature of terrain

A rugged terrain will require a larger interval than gentle rolling country.

Layering tinting system

A scale of graded color tints or a system of different colors is used to show different zones of elevations.

Total stations 20-40 acres

A very large percentage of topographic surveys today are made with total stations. The instrument which is used for almost all topographic surveys of small areas. Up to ___________________

Index contour

As a convenience to scaling elevations and to provide ease and speed in reading contours, shown by a heavier line at regular intervals on a topographic map.

Global positioning system

Become the common tool of today's surveyor. Combined with a realtime or post-processing error methods, highly accurate surveying and mapping results can be rapidly obtained.

Transit-stadia or theodolite-stadia method

Classical or historical method of gathering topographic data, the necessary measurements were made in the field, recorded in the field and book and then plotted on paper in the office.

Layer tinting system

Color tints when used in conjunction with contour lines give pictorial effect by accentuating the areas of different elevations.

Layering tinting system

Common use for aerial navigation charts and on a small scale maps of the world.

Foresters

Locate access​ road or haul-roads, fire control routes observation towers.

1. By estimation 2. Rubber band method 3. Analytical method 4. Triangle and Scale Method 5. Template method.

Locating contour lines

Topographic maps

Made to show this information, together with the location of artificial and natural features of the earth, including buildings, highways, stream, lakes, forests and etc.

Ridge and stream lining

Mainly used to emphasize the location of low and high ground. This method is especially used in aerial photographs.

Rubber band method

Method of locating contours with the aid of rubber band, it should be sufficiently wide such that graduations at equal intervals can be marked on it to form some kind of elastic scale.

Contour lines

Most widely used method of quantitatively representing hills, mountains depressions and ground surface undulations on a two dimensional sheet of paper.

Tracing contour method.

Occasionally used when the transit-stadia method was common with these procedure. A number of points were located whise elevations were equal to those of desired contour.

Shading

Old method used to show relative elevations on map.

1. Point density allows an accurate plot of contour lines. 2. Diff. Conditions call diff. Point densities 3. Points should be chosen along hills to make break lines 4. Point can also be uses to locate monuments in the field

Point selection for topographic surveys:

Monuments

Points should also be placed around prominent objects that di not move

Relief or terrain models.

Provide the most striking and realistic expression of topography.

Spot heights

Provides definite and precise information regarding elevation.

1. Relative cost 2. Purpose of the map 3. Nature of terrain 4. Scale of the map.

Selection of contour intervals

1. Checkboard method 2. Controlling point method 3. Tracing contour method

Selection of points for topographic map

Hachures

Series of short lines drawn in the direction of slope.

Contour Lines or Isohypes

Shown on maps as the traces of level surfaces of different elevations. Contains the shape of various topographic features.

Relative cost.

The smaller the interval, the greater is yhe amount of fieldwork. The cost of the map will be higher as the contour interval is reduced.

Form lines

These lines are sketched from visual observation from inadequate or unreliable map sources.

Supplemental/ Auxiliary Contour

They are drawn as dashed lines or lines of dots that begin and end when they approach the areas where the regular contours close on each other.

Relief or terrain models.

They are made from wax, clay, plastic, cardboard and other materials and shaped to agree with actual terrain.

Cartographers

They are the designers of contour map.

Index contour

They are usually drawn every fifth contour and carry the contour number or elevation designation.

Shading

This method is accomplished by correct placement on the map of different shades of gray tints.

Analytical method

This method is suitable for drawing large scale maps also, it is assumed that the slope between two adjacent established points is uniform.

By estimation

This method is suitable for small scale maps where the ground form is not too irregular, wherein contour lines can be located with the given two contour elevations.

Triangle and scale method

This method provides accurate and rapid procedure for interpolating contour lines in which mathematical computations are eliminated.

Computer-aided contouring

Today programs are available to perform the necessary calculations and plot the contour lines and other details quickly and accurately with personal computers.

Photogrammetry

Used for topographic maps of larger areas.