Measuring the Earth
This line at 0° latitude divides Earth into the Northern and Southern Hemispheres.
What is the equator?
This systematically renders locations from Earth’s curved surface onto a flat map surface.
What is a map projection?
This map element explains the meanings of symbols and colors.
What is a legend?
Tracing features from a source map into a digital format is this process.
What is digitizing?
GPS belongs to this broader family of satellite-based positioning systems, abbreviated GNSS.
What are Global Navigation Satellite Systems?
These lines measure angular position east or west of the prime meridian.
What are lines of longitude?
Area and shape are the two major map projection properties. These are the two minor properties.
What are distance and direction?
Unlike a reference map, this kind of map emphasizes one subject.
What is a thematic map?
A digitized line stops short of the line or node it should connect to, creating this error.
What is an undershoot?
Orbiting satellites, monitoring stations, and receivers belong to these three GPS segments.
What are the space, control, and user segments?
This model has a semi-major axis in the equatorial direction and a semi-minor axis in the polar direction.
What is an ellipsoid?
To compare the sizes of countries fairly, a cartographer chooses this projection property, which preserves area relationships.
What is equal area?
A map of land-use categories is qualitative. A map showing population counts belongs to this other type of thematic map.
What is quantitative?
These intermediate points define a line’s shape between its starting and ending nodes.
What are vertices?
A satellite signal bounces off a building before reaching your receiver, producing this error.
What is multipath?
A benchmark has different coordinates in NAD27 and NAD83. This operation converts its position from one datum to the other without physically moving it.
What is a datum transformation?
This tool uses tiny circles on Earth’s surface to reveal distortion by showing how their shapes and sizes change when projected onto a map.
What is Tissot’s indicatrix?
“One inch on the map equals one mile on the ground” expresses scale in this format.
What is a verbal scale?
Also called registration or georectification, this process uses control points to bring spatial data into an Earth-based map coordinate system.
What is a coordinate transformation?
This positioning method uses a base station at a known location to help correct a rover’s observations.
What is differential GPS?
Unlike the mathematical ellipsoid, this irregular reference surface follows equal gravity potential and approximates global mean sea level.
What is the geoid?
These lines mark where a developable surface intersects the ellipsoid and map scale is true. When they follow latitude, they are called standard parallels.
What are standard lines?
These six map elements show the subject, mapped features, symbol meanings, distances, orientation, and data sources.
What are the title, map body, legend, scale, directional indicator, and metadata?
To register a map accurately, these points should be stable, identifiable, and evenly distributed throughout the mapped area.
What are control points?
Two observation sessions have similar ranging errors, but PDOP values of 2 and 7. This session has the more favorable satellite geometry.
What is the session with PDOP 2?