Contours, GPS, Map Data, and Cartography
Contours and Profiles
Contours and Profiles: What is the process of contouring?
What is a Contour/Isoline?
A contour, or isoline, is a line that connects data points of equal measure, such as points of equal elevation. Contours indicate elevation and changes in elevation. Almost any type of variable that occurs in the natural world can be represented with isolines.
Rules for Drawing Contours/Isolines
- Lines cannot cross one another.
- Lines typically extend to the edge of the map and must have a label indicating the measured value (e.g., feet, temperature).
Types of Information Displayed Using Contours
Contours are commonly used to display natural phenomena such as elevation, precipitation, and temperature.
What is a Profile?
A profile is a cross-sectional view of the terrain along a transect (a line from point A to point B). It shows the lay of the land from the side, making it easier to visualize changes in the landscape. The profile illustrates how the shape of the land changes between two points, indicating hills, valleys, steep slopes, and gentle slopes.
What is Vertical Exaggeration?
Vertical exaggeration is used because horizontal distances greatly exceed vertical distances. If a profile were drawn to the same scale as the map, it would be impossible to read. Vertical exaggeration is calculated by dividing the map scale by the vertical scale.
Example:
On a standard topographic map with a map scale of 1:24,000, 1 inch equals 24,000 inches (or 2,000 feet). This is the horizontal scale. If a vertical profile is created with a vertical scale of 1:1,200 (1 inch equals 1,200 inches or 100 feet), the vertical exaggeration is 24,000 / 1,200 = 20. The profile is exaggerated by a factor of 20.
Global Positioning Systems (GPS)
What was the Modern Precursor to GPS?
Transit was the first GPS-like application, used to provide precise guidance to Polaris nuclear missile submarines. Ballistic missile submarines needed multiple means of guidance as they were not supposed to surface, and the missiles required precise guidance.
Sources of GPS Error
- Electromagnetic interference: Interference from other electromagnetic sources.
- Signal multipath: The signal is reflected off objects such as tall buildings or large rock surfaces.
- Receiver clock error: Receivers do not have the atomic clocks that satellites have.
- Orbital error: Inaccuracies in the satellite’s reported location.
Maps: Data and Charts
Data Types
- Nominal: Divides a group into subgroups (e.g., male/female, eye color).
- Ordinal: A numerical sequence that puts things in order (e.g., event 1, event 2, event 3; height ranking).
- Ratio: Uses a regularly spaced scale with a true zero starting point (e.g., timeline). All mathematical calculations can be performed.
- Interval: The starting point is arbitrary (e.g., temperature, latitude, and longitude).
Chart Faults
One example of a chart fault is a 3D pie chart, which is hard to interpret. Another common fault is when the Y-axis does not start at zero, which can distort the data representation.
Choropleth Maps
A choropleth map uses existing political boundaries to display data. Data within these boundaries are mapped and color-coded by amount or magnitude.
Cartographic Propaganda
How Cartographic Propaganda Maps Achieve Their Goals
- Propaganda maps sell ideology, shape opinions, and promote allegiance.
- They use advertising techniques to make the map intriguing and draw in the user.
- Many people trust maps outright and do not question their accuracy.
- Selection and generalization are done with an agenda, often involving the fraudulent selection of data.
The Peters Projection and Its Goal
The Peters Projection was developed to “right a wrong” and raise awareness of the plight of equatorial third-world countries. It challenged the Mercator projection, which was perceived as distorting the size of northern hemisphere industrialized countries. The goal was to promote a more equitable representation of less industrialized countries.