7 - Vertical Position
PANDAPAS POND Forest Legend Maps and Mapping
Topic 5: Vertical Position
Course: GEOG 2314 Representations of Relief
Vertical Position
Maps, both 2D and 3D, represent a three-dimensional surface.
Horizontal location and vertical value (elevation/height).
3D maps feature a raised surface that directly indicates vertical position.
2D maps can use perspective techniques to appear three-dimensional or employ symbols for 3D effect.
Levels of Abstraction in Depicting Relief - I
Relief Models
Range from globes showing mountains to small regions on molded plastic sheets (true 3D models).
Relief Models
Require both horizontal and vertical scales.
The vertical scale does not need to match the horizontal scale.
Vertical Exaggeration (VE)
Defined as the relationship between vertical and horizontal scales on relief models or 2D perspective maps.
VE is a Function of Horizontal Scale
Example: For a bowling ball relief without vertical exaggeration, what would Mt. Everest's height be?
A 1:63,360 scale (1 inch = 1 mile) results in a 2,500’ mountain being 0.48” high.
A 1:63,360,000 scale (1” = 1 thousand miles) makes the same mountain 0.00048” high.
Smaller horizontal scales necessitate greater vertical exaggeration to maintain audience interest!
Computing Vertical Exaggeration
VE is expressed as:
n-1: A VE of 20 – 1 indicates the vertical scale is 20x the horizontal.
Formula: VE = Vertical Scale / Horizontal Scale
Levels of Abstraction in Depicting Relief - II
2D Perspective Drawing Maps
Techniques include:
Hypsometry
Block Diagrams
Plastic Shading
Fishnets
These techniques create 3D appearances in a 2D format and may involve vertical exaggeration.
Hypsometry
Usage of colors to represent height:
Blues for water (darker signifies deeper areas).
Green for lowlands.
Yellow-Brown for medium elevations, transitioning to reds at high elevations.
CANADA Relief in Metres
Notable peaks include Mt. Logan (5,959 m).
Elevation range and sea level depicted.
Hypsometry - Common Techniques
Hypsometry is widely used for small scale maps and is based on how colors focus differently at varying wavelengths due to psychological principles of advance and retreat.
Levels of Abstraction in Depicting Relief - III
Contours and Spot Heights
This method is more absolute rather than relative as seen previously.
Utilizes base or datum levels with multiple contours on the same map based on objectives.
Base/Datum Levels
MSL: Mean Sea Level (Geoid).
MLW: Mean Low Water (Typical low tide).
MHW: Mean High Water (Typical high tide).
Different levels serve specific purposes in topographic maps.
Interpolation
Method to determine values (elevation, temperature, etc.) between contour lines on isarithmic maps.
Estimation is bounded by the values of adjacent lines.
Elevation Formula
Elevation = Starting Contour Value +/- X Contour Interval
A is the number of 50ths from starting contour to the measurement point.
B is the perpendicular distance between the two bounding contour lines.
Interpolation Technique
The goal is to estimate distances along the steepest slope, represented by a gradient line (perpendicular to contour lines).
Interpolation Method Steps
Locate the point in question.
Draw a perpendicular line to contour lines.
Measure length to the point (B) and the distance from lower contour (A).
Assumptions in Interpolation
Constant slope along the gradient line.
Value to determine is between values at the two contour lines.
Error will be less than one contour interval (usually ½).
Extrapolation
Used when contours are missing either side of the point.
Assuming a continuation of the slope to estimate values.
Blacksburg Practice
Measure elevations at various specified locations in Blacksburg.
Alaska Practice
Measure elevations at various specified locations in Alaska.
Homework Assignment
Homework 5: Elevation measurements with 8 questions covering locations from Alaska and Blacksburg.
Quiz 5 on horizontal position, open until Sunday night.
Quiz 6 covering vertical position, also open until the next Sunday night.