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Topographic SurveysTopographic Surveys

Topographic mapsTopographic maps

• Vertical data (elevation height) are theVertical data (elevation, height) are the distinguishing characteristic of topographic mapsmaps

• Topographic maps show the configuration or shape and roughness of the ground; thisshape and roughness of the ground; this roughness is commonly referred to as reliefTh h i d i i f h li f f• Throughout time, depiction of the relief of a parcel of land has changed

3Topographic Surveys; Prepared by Andre‐Paul C. Ampong

Topographic surveysTopographic surveys

• Topographic surveys involve all procedures, opog ap c su eys o e a p ocedu es,equipment and methods necessary to capture both horizontal and vertical data of points on the

d ll h d hground so strategically chosen to depict the terrainM d t hi t i t th t• Modern topographic maps represent points that have identical elevations with lines called “contours”contours

• The elevation on these lines are based on known or assumed datum


Sugar loavesSugar loaves

• These are idealized depiction from a side orThese are idealized depiction from a side or oblique view; the only form of topography on early maps (pre‐1700) due to lack of detailedearly maps (pre 1700) due to lack of detailed surveying; gives location of mountains/hills but not precise sizebut not precise size.


HachuresHachures

• Hachuring use lines of varying width and length g y g gto depict slope steepness, drawn in direction of the slope. Initially unsurveyed and little better than sugar loafs the first form known givingthan sugar loafs, the first form known giving general location of mountain ranges are referred to as 'hairy caterpillars‘

• In modern maps, hachures are not often used except when the scale of the map is too small to permit contouringpermit contouring

• If properly drawn, they convey a good concept of the terrain, but their value is largely pictorial


HachuresHachures


HachuresHachures• They were systematized in 1799 by Major Lehmann, an Austrian military officer, where line width became directly proportional to steepness. It hence became quite commensurable, but not very imageable: blank q y gon top and in valleys, and shortly after a North‐West light source was introduced to enhance imageability. This was the main type of relief depiction through the yp p g19th century

• After accurately surveyed heights became available through the 20th century hachures gave way tothrough the 20th century, hachures gave way to contours, but they are still used for very steep slopes such as cliffs, quarries and railway cuts, where contour lines would mergelines would merge.


HachuresHachures


HachuresHachures

• Disadvantages:Disadvantages: – Lack of absolute information– Difficulty in distinguishing the direction of the slopeDifficulty in distinguishing the direction of the slope – Time‐consuming to produce– Obscures other informationObscures other information– Not very effective except in mountainous terrain

• AdvantageAdvantage– They may show minor but important details otherwise lost on a contour map within the contour intervals


HachuresHachures


ContoursContours

• Contours came initially from the need to know Co tou s ca e t a y o t e eed to oexact depths in water, and were generated from a series of depths or soundings. The first contours

h l ’ hin the late 1900’s were on navigation charts as 'isobaths' (since hachuring was not suitable for an unseen landscape)unseen landscape).

• A contour is essentially an isarithm or an isopleth: a line drawn on a map through all pointsisopleth: a line drawn on a map through all points having the same numerical value, as of a population figure or geographic measurement


ContoursContours


ContoursContours

• Characteristics: – Contour interval (the distance between contour lines) is determined by terrain and map scale I d b li d id li d– Index contours are symbolized as wider lines and usually every 5th contour

– Form lines are approximate elevations (not o es a e app o a e e e a o s ( oaccurately surveyed)

– Depression contours (enclosing lower land) are drawn with small tick marks insidedrawn with small tick marks inside.


ContoursContours

• Basic rules– A contour line must never split or divide.– A contour line must never simply end except at the edge of the map.

A contour line must represent one and only one elevation– A contour line must represent one and only one elevation. – A contour line may never intersect other contour lines. Overhanging

cliffs are the only exception. C li f i l i– Contour lines from a V‐pattern crossing stream always points upstream.

– Closely spaced contour lines represent a steep slope, widely spaced li i di l llines indicate a gentle slope.

– Concentric circles of contour lines indicate a hilltop or mountain peak. – Concentric circles of hachured contour lines indicate a closed

depression.


ContoursContours


ContoursContours

• Advantages g– it is the most commensurable (quantitative) method – it is the origin for many (most?) newer depiction techniques and it is now familiar to many userstechniques, and it is now familiar to many users.

• Disadvantages – it is an abstract method (there are no counterpart to ( plines on ground); poorly suited to small scales

– less imageable but depending on: contour interval, map scale, landscape type, and users' experience.map scale, landscape type, and users experience.

These disadvantages were recognized early on and led to other methods being developed .


Hypsometric tintsHypsometric tints

• The addition of colour to elevation levels firstThe addition of colour to elevation levels, first tried as early as 1830. Color schemes require graduation logical sequence realistic colorsgraduation, logical sequence, realistic colors, with the darkest still able to bear readable texttext.



• Advantages g– adds imageability, mostly at small scale; easily applied and understood

• Disadvantages• Disadvantages – exaggerated terrace effect, no new real 'information' is added,

– differential contrast between tints and other elements, dubious color associations, (green with forest, etc.) (g )

– which colour scheme?.. chroma of the same hue, or spectrum range ‐ green ‐> yellow ‐> red


Shaded relief (hill shading)Shaded relief (hill shading)

• This involves the addition of shadows to giveThis involves the addition of shadows to give the illusion of depth, assuming a theoretical NorthWest light source (at 45 degreesNorthWest light source (at 45 degrees elevation). It was introduced in the 1900’s but became more widespread after 1960 withbecame more widespread after 1960, with improved printing technology and user needs. It has become much more common withIt has become much more common with automation.



• Advantages g– highly imageable, continuous in appearance (as in reality), can show greater detail and character of landscapelandscapesuitable over a variety of scales and as a general background for a variety of map types

• Disadvantages – Manually required artistic creation with pencil or airManually required artistic creation with pencil or air brush; It was costly and often poorly rendered, when done manually. It creates a variable background with some slopes very darkp y


Tanaka (relief) contoursTanaka (relief) contours

• This technique of applying a northwest light s tec que o app y g a o t est g tsource to a contoured landscape was first tried in 1850 but printing methods then could not handle

b k d ( b bl h hl hgray backgrounds (to be able to highlight illuminated lines).

• It was pioneered from the 1950s by Kitiro Tanaka who produced some exquisite examples using thewho produced some exquisite examples using the theory of application of shading principles to contouring.


Tanaka (relief) contoursTanaka (relief) contours


Block (perspective) diagramsBlock (perspective) diagrams


Block (perspective) diagramsBlock (perspective) diagrams

• Advantage:Advantage:– the most imageable portrayal of landscape (3D), often used for ski hills and panoramasoften used for ski hills and panoramas

Di d t• Disadvantages– the most time‐consuming to produce with no

i t t li l (b f t )consistent linear scale, (before computers)


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