Intro to Map Use Study Outline

Contour Interpretation & Topographic Features

You should be able to:

1. determine the elevation of any point on a contour map

2. draw a profile along a line on a contour map

3. calculate the slope of a hill using a contour map

4. describe the main features of the landscape from a contour map

A. interpreting contours

a. basic features

i. always check the contour interval first

ii. highest points are closed loops

iii. closely spaced contours are steep slopes, wider spaced lines are gentler slopes

iv. valleys generally have V shaped contours with the point of the V pointing upstream

v. ridges are U to V shaped with the open part facing uphill

2. elevation calculation of a point

i. if point is on a contour line, find the nearest labeled index contour and count contour intervals up or down as needed

ii. if point is between contour lines, assume the slope is straight between the contours and interpolate, e.g. if the point is 3/10ths of the distance from the lower to the higher contour lines then add 0.3 X contour interval to the lower lines elevation

c. profile

i. shows changes in elevation along a line or route of interest

ii. measure and mark distance between contour lines along path on the x axis of a graph

iii. mark elevation of each contour line on the y axis

iv. connect the elevation marks to show the ups and downs along the path

d. slope

i. measure horizontal distance and elevation change along a path of interest

ii. unless a route is specified (e.g. the slope of a road) slope is assumed to mean the steepest path up a hill, which is always perpendicular to the contour lines

B. landscape features

a. Rivers chacteristics

i. river profile

ii. drainage pattern

1. pattern created by tracing all connected stream channels

2. indicates characteristics of underlying rocks

iii. texture of dissection

1. relative number of stream channels in a given area

2. indicates how porous underlying rocks are, few streams means precipitation soaks in rather than flowing over surface, creating valleys

iv. U shaped valley indicates glacier carved valley

v. V shaped valley indicates river carved valley

vi. meanders

1. indicates a stream that has carved as deep as it can in current climate

2. create distinctive flood plain features

C. Uplands areas

a. old landscape in a wet climate

i. exposed to weathering and erosion for 100s of thousands or more years

ii. smooth and rounded

iii. flat land only in low lying areas

iv. no lakes

v. shows pattern of underlying structures of bedrock

b. new landscape (created 10s of thousands of years ago or newer)

i. formed by major event – volcano, glacier, earthquakes..

ii. lakes

iii. flatlands w/deep valleys

iv. no organized drainage pattern

D. Mountains

a. volcanic - isolated cones and peaks

b. from folding and faulting – ranges of similar sized peaks