GIS 10/9

What is the difference between raster and vector data models?

Vector data uses discrete coordinates (points, lines, polygons). Raster data uses a grid of equal-sized cells (like imagery or elevation).

What are the three basic types of vector data?

Points, Lines, and Polygons.

What makes vector data "smart"?

Every feature has a unique ID (ObjectID or FID) that links to a row in an Attribute Table.

What is a Shapefile?

An older vector format made up of multiple files (.shp, .dbf, .prj) that must be moved together.

What is the difference between Continuous and Discrete raster data?

Continuous rasters have gradually changing values (elevation, temperature). Discrete rasters represent distinct categories (1=forest, 2=water).

What are the components of a spatial reference?

A geographic coordinate system (datum), a projection (if projected), and coordinate units.

What is the difference between a Geographic and Projected coordinate system?

Geographic uses a 3D spherical surface with units in Degrees. Projected uses a mathematical transformation to flatten the map into a 2D surface with units in Meters/Feet.

What is geodesy?

The science of measuring the exact size, shape, and gravity field of the Earth.

What is the difference between the Ellipsoid and the Geoid?

The Ellipsoid is a smooth, mathematically perfect oval-sphere used for GPS. The Geoid is a bumpy, irregular model based on gravity and global mean sea level (used for true elevation).

What is a Datum?

A reference frame that pins the math model (ellipsoid) to the actual Earth so coordinates line up correctly (e.g., WGS84, NAD83).

What are the three main projection families?

Cylindrical (good for global), Conic (good for mid-latitudes), and Azimuthal/Planar (good for poles).

What is the difference between Conformal and Equal-Area map projections?

Conformal preserves local shapes but heavily distorts size (Area). Equal-Area preserves true size but distorts shapes.

What is Tissot's Indicatrix?

A tool used to measure map distortion by placing perfect circles on a 3D globe and seeing if they turn into ovals (shape distortion) or change size (area distortion) when flattened.