Week 4 and 5

Raster data model

A model that contains pixels, cells, and grids.

Raster properties

Extent (#rows, # cols), Resolutions (cell size), and location.

Stacks

Combine multiple raster layers

Implications of cell size

Smaller cell sizes offer greater precision but lead to larger file sizes; larger cell sizes provide less accuracy but are faster to analyze.

Lossy Compression

does not maintain original pixel values

Non-Lossy Compression

retains the original digital number pixel values.

When should Raster data be used

Better for spatial analyses that cover extensive areas.

When should Vector data be used?

Preferable for topological and network analyses.

Data conversion issues

Small features can be lost entirely if smaller than the cell size during conversion.

Datum

A reference surface or model of Earth used for plotting locations.

Geodesy

The science of measuring Earth’s shape to develop models like geoid and ellipsoid.

Geographic coordinate system (GCS)

Defines where data is located on the earth’s surface.

Projected coordinate system (PCS)

Tells how data should be displayed on a flat surface like a map.

Developable surface

A surface that can be flattened to a plane without distortion.

Projection

The visual representation of spatial measurements on a different surface.

Universal Transverse Mercator (UTM)

A coordinate system for mapping.

Types of developable surface

Planes, cones, and cylinders.

Geoid

A hypothetical Earth surface representing mean sea level without external influences.

Distortion types in projections

Shape, area, distance, or direction.

Vertices

Points that define the shape of a line.

Nodes

Endpoints of a line.

Common editing errors

Errors include undershooting, overshooting, dangling nodes, pseudonodes, missing label points, and line crossings without nodes.

Line Snapping

A process where a vertex or node gets 'snapped' to a line or endpoint when they are close.

COGO

Coordinate Geometry, a method of defining and analyzing spatial relationships.

Mercator

Used for navigation, but distances and areas are distorted near the poles 

Equidistant

Distances are true only along certain lines, but shapes are distorted 

Equal area

Preserves area, but shapes are skewed

Conformal

Preserves angles locally, but areas and distances are distorted 

Lambert Conformal Conic

A standard projection for mapping large areas in the mid-latitudes, such as the United States, Europe, and Australia 

Transverse Mercator

Used for zones running north and south 

Pyramids

improve raster performance by allowing different levels of detail.