Topography

Topographic map

1) Graphical portrayal of topography 2) Shows earth's surface characteristics such as hills and valleys, and constructed features 3) Shows horizontal distances and elevation above a given datum between features

Considerations in Topographic Survey

1) Purpose 2) Map scales and contour intervals 3) Accuracy and degree of detail 4) Horizontal control 5) Vertical control 6) Reference datum

Hachures

Consists of rows of short, nearly parallel lines whose spacing, weight and direction produce an effect similar to shading.

Illuminated contours

Contours are drawn as if they was a light shined from the northwest. Contours are emphasize

Profiles

Cross-sectional views

Intermediate contours

Defined as lighter weight contours found in between index contours

Contour Intervals

Difference in elevation between two adjoining contours

Layer Tints

Each elevation zone is indicated by printing a distinctive color between bounding contours Lighter tones - higher elevations Darker Tones - Lower elevations

Applications of contours

Elevation estimation, reservoir capacity estimation, flood zone maps, intervisibility between points

Form Lines

Estimated contours

Index contours

Every fifth contour (0m,5,10,15, 20 -index contour) in which line thickness is heavier. Contains the number to designate elevation

Approximate

For areas where the elevations are not accurately determined

Spot Heights

Indicates the elevations at particular points.

What is the relationship between contour distance and slope?

Inverse relationship

What are the characteristics of contours on a plane surface?

Straight and parallel

Topography

The configuration or shape and roughness of the ground

Colors of contour lines

blue for areas below sea level, brown for regular

Disadvantage of GPS

has to transform ellipsoidal heights (from a reference ellipsoid) to orthometric value (from a geoid)

Ridge and Stream Lining

- Emphasizes location of high and low ground, and used as an overlay in aerial photographs and topographic maps - Main streams are drawn in solid blue - main ridges are drawn as brown dashed lines

Purpose

- Gather data necessary for the construction of a graphical portrayal of planimetric and topographic features

Supplemental contours

Used in areas that are flat so that contours are far apart. Dotted lines

Depression contours

Used to show low spots. Ticks point downhill.

When can contours merge?

Walls or overhanging cliffs

When should you use Hachure Lines?

When relief cannot be sufficiently expressed by contours because of steep slopes.

Contour Lines

A line joining points of equal elevation on the map.

Topographic Survey

A process of determining the positions, on the earth's surface, of the natural and man-made features of a given locality and in determining the configuration of the terrain

What are the factors affecting contour intervals?

Accuracy, features, legibility, cost, use of map

Shading

An assumed light source from the NW is imagined as creating areas of light and shadow. Continuous areas

Reference datum

Mean Sea Level

Block Diagram

Pictorial representation of the surface, drawn from space

Subaqueous contours

Portrays ground underwater

Methods for locating topo details

Radiation by TS, radiation by stadia, coordinate squares, offsets from a reference line, GPS detailing

Project control for Topo Surveys

Reference framework should have 2+ permanent control points

Relief model

Representation of the terrain done in 3D to suitable horizontal and vertical scales

What do irregular contours signify

Rough, rugged terrain

True or false: All contours must close within or outside the map borders

True

Locating topographic details

Tying mapping details to the control network

What direction do contours point in rivers?

Upstream

On uniform slopes, the contours are ____ spaced

uniformly