Contour Interpretation

topography or hypsography

refers to the configuration and roughness of the ground. It tells whether the ground is flat, hilly, or in between.

Relief Representation

This type of information is shown in topographic maps and usually presented with existing natural or artificial features on the ground.

Hachures

are small lines drawn to represent slopes.

thicker, thinner

The lines are drawn ______ to represent steeper slopes and _______ for gentle slope.

black

The slopes above 45° is depicted completely in ______ color.

45 degrees

The slopes above _____ is depicted completely in black color.

Contours

are imaginary lines connecting places having same elevation above mean sea level.

Contours

They are drawn usually brown color.

Brown

Contours are usually drawn in ____ color

Index contour

is a contour line containing the elevation tag, and is usually drawn thicker than the other contour lines

Contour interval

is the vertical distance between two adjacent contours.

Form lines

are like contours representing features in an estimated manner, and are shown by broken lines

Layer coloring (layer tinting)

is a method showing relief in layers and each layer is given a different color.

Layer coloring (layer tinting)

It is the method by physical atlas maps.

Blue

Ocean depth is also shown in various shades of ____

Blue

Color representing bodies of water

Green

Color representing plains

Brown

Color representing highlands

White

Color representing snow covered peaks

Hill Shading (levels of gray)

is a method of representing relief on a map by depicting the shadows that would be cast by elevated areas if light were shining from a certain direction.

Are heights of places surveyed and they denote the actual height above mean sea level.

Spot heights

It is usually represented with a dot and elevation 9in meters) next to the dot or triangle.

Index contour

This line facilitates reading the topographic map because the elevation of contour line is written in a break, and usually drawn in heavier or thicker line.

Intermediate contours

These are contour lines between two index contours and usually drawn as finer lines compared to index contour.

Depression contours

These are drawn to show low spots in the area such as excavations or volcano crater, and represented by drawing lines or ticks perpendicular to the index or intermediate contours that are close

Hill

represented by a concentric series of closed lines

Depression

indicated by hachure marks on the downhill side

Supplemental contour

These types of contours are used when the elevation change in minimal, such as in flat terrain or floodplains and usually drawn in broken or dashed lines between intermediate contours.

Approximate contours

are drawn when contour accuracy cannot be determined on the ground due to inaccessibility or when it is difficult to derive contours from aerial photographs because of cloud cover or shadows on the photos.

Approximate contours

These are mainly estimates or approximation of contours based on the educated guess of the map maker instead of leaving the area as blank.

Contour interval

The constant vertical distance between two adjacent contour lines

Flat to gently rolling

1-5 contour interval

Hilly

5-20m contour interval

Mountainous

25-100 contour interval

Tracing contours method

This method is used when the exact location of a particular contour line is required.

Tracing contour method

It is effectively performed by use of the plane table, but can be done by azimuth-stadia survey method

Cross-section method

This method is suitable for preparing strip maps which can be accomplished by using level and tape or azimuth-stadia.

Cross section

are taken at right angles to a centerline or baseline.

Cross section method

Elevation of each shot are written on the strip map, and interpolation of contour lines is performed in similar manner as in grid and controlling point methods.

Controlling points method

This method is suitable for maps of large area and small scale. The selection of ground points is very important in conducting topographic survey.

Shots should be taken at stream junctions, at intermediate points in stream beds between junctions and along ridge lines. Field notes should indicate these points so that ridges and streams can be plotted before interpolations are made. Interpolation process is done in similar manner as in grid method.

Grid method

is very effective in locating contours in relatively small area and fairly uniform slope.

Grid Method

To do this, the area is divided into squares or rectangles of 5-20 meters, depending on the map scale and desired contour interval. Dividing lines are numbered accordingly for easy reference and recording of data in field notebook. Then elevation of intersection points between dividing lines (or vertices of square) are determined in the field.

Inverse ratio

The contour interval should be in ____ to the scale of the map