UNIT 3 – MODULE 2: Spatial Data

DATA Sources of data can be categorized as primary (first-hand observation or secondary (collected by someone other than the user). All data sources have three modes or dimensions: – Temporal – Thematic – Spatial Credit: CSU - Chico

MODES & DIMENSIONS Temporal – Records when data was collected. Example: 02:30 hours, 4 March, Thematic – Describes characteristics of the data being referenced. Example: dry slab avalanche caused by three skiers. Spatial – Coveys information about a location or feature. Example: Snow Valley, north- facing slope.

MAPS How we traditionally store, analyze and present spatial data. Can take different forms. Thematic maps – shows data or information about a specific topic or theme. Maps are generated with a purpose or goal. Credit: EIA Credit: University of Delaware

SCALE Maps are always smaller than what’s being presented. Scale allows us to get a real- world sense of features on a map by comparing actual size to a represented size. We express scale in three different ways: – Ratio Scale – Verbal Scale – Graphical Scale Credit:

POINTS Represents features that are too small to be represented as with the map scale being used. Example: tree, lamp post, mailbox, etc. Data from a point should include location, height and feature details. Credit:

LINES Represents linear features (e.g. rivers, roads, power lines, geologic fault lines). Credit: ArcGIS

AREAS Represented by lines that enclose a portion of the map (e.g. buildings, lakes, fields, parks). Can also represent features that do not exist (e.g. school zone). Areas are commonly referred to as polygons. Credit: GIS Consortium

GENERALIZATION All spatial data is a generalization of real- world features. Simplifying real-world features is necessary for map clarity. Amount of detail will be determined by the map scale. Credit: Ordnance Survey

GENERALIZATION EXAMPLE Example: Bloodvein River Small Scale Representation – Bends & Turns Smoothed – Simplified & Easy To Read Large Scale Representation – More Details – Nearby Features Highlighted – Complex Credit:

SPATIAL REFERENCING Referencing system needed for locating features on Earth’s surface. There are several spatial referencing categories: – Geographic Coordinate Systems – Rectangular Coordinate Systems – Non-Coordinate Systems (e.g. Zip Codes) Geographic coordinates (latitude & longitude) are the most common. Credit: ArcGIS

DATA SOURCES Spatial Data – Census & Survey Data (Population Census, Employment Data, Marketing Data, etc.) – Aerial Photographs – Satellite Images Field Data – used when data does not exist. – Surveying – GPS Some data sources may be more accurate than others. Which do you think is more accurate: census data or satellite images?