Earth's Coordinate System and Mapping
The Latitude-Longitude Coordinate System
Latitude is the angular distance north or south of the Equator, measured in degrees.
Longitude is the angular distance east or west of the Prime Meridian, also measured in degrees.
The Equator is the only line of latitude that is a great circle, dividing Earth into the Northern and Southern Hemispheres.
Parallels of Latitude
- Parallels are east-west circles on Earth's surface, parallel to the Equator.
- They are measured in degrees from 0° at the Equator to 90° at the poles.
Latitude is positive in the Northern Hemisphere (e.g., 41° N) and negative in the Southern Hemisphere (e.g., 41° S).
To remember latitude, think of the Equator as a "ladder" (sounds like "latitude") that circles the globe horizontally.
Meridians of Longitude
- Meridians are north-south lines that converge at the poles.
- The Prime Meridian (0° longitude) runs through Greenwich, England, and serves as the reference line for measuring longitude.
Longitude ranges from 0° to 180° east or west of the Prime Meridian.
Longitude lines are not parallel; they converge at the poles. This is why the distance between meridians decreases as you move from the Equator toward the poles.
Determining Latitude and Longitude
- Latitude: In the Northern Hemisphere, latitude can be determined by measuring the altitude of Polaris (the North Star). The angle between Polaris and the horizon equals the observer's latitude.
- Longitude: Calculated by comparing local noon (when the Sun is highest in the sky) to the time at the Prime Meridian. Each hour of time difference corresponds to 15° of longitude.
* If local noon occurs 3 hours after noon at Greenwich, the location is 45° west of the Prime Meridian (3 hours × 15°/hour).
Don't confuse latitude and longitude. Latitude lines run horizontally but measure north-south positions. Longitude lines run vertically but measure east-west positions.
Mapping Earth's Surface
Maps as Models
- A map is a two-dimensional representation of Earth's surface.
- Maps use symbols, scales, and coordinate systems to convey information.
* A map scale of 1:100,000 means 1 unit on the map equals 100,000 units on the ground.
Field Maps and Isolines
- A field is a region where a measurable quantity (e.g., temperature, elevation) exists at every point.
- Isolines connect points of equal value:
- Isotherms: Lines of equal temperature.
- Contour lines: Lines of equal elevation.
The spacing of isolines indicates the gradient (rate of change). Closer lines mean a steeper gradient.
When reading a topographic map, remember that contour lines form a "V" shape pointing upstream when crossing a river or stream.
Topographic Maps
- Topographic maps show elevation and landforms using contour lines.
- Contour interval: The vertical distance between contour lines.
* If the contour interval is 10 meters, each line represents a 10-meter change in elevation.
Contour lines never cross, except at vertical cliffs, and they form closed loops (even if the loop extends off the map).
Map Symbols and Direction
- Symbols: Represent features like rivers, roads, and buildings.
- Direction: Most maps are oriented with north at the top. Arrows may indicate magnetic north (MN) and geographic north (GN).
Use the map's scale to measure distances accurately. For example, if the scale is 1:50,000, 1 cm on the map equals 500 meters on the ground.
Constructing Map Profiles
A map profile is a cross-sectional view of the land between two points.
- Draw a line between the two points on the map.
- Place a strip of paper along the line and mark where it intersects contour lines.
- Transfer these marks to graph paper, using the contour interval to determine elevation.
- Connect the points with a smooth line to create the profile.
When drawing a profile, ensure the vertical scale is consistent with the contour interval to avoid exaggerating the slope.
Applications of Earth's Coordinate System and Mapping
- Navigation: Latitude and longitude are essential for GPS and maritime navigation.
- Environmental Science: Field maps track changes in temperature, pollution, and other variables.
- Urban Planning: Topographic maps guide infrastructure development by showing elevation and landforms.
