W1 Flashcards
What is geographic data?
A computer based representation of the real world.
What kind of decisions must one make when creating representation with GIS?
- data formats
- data structures
- types of data
- accuracy and precision
- Uncertainty
- etc…
What are the 3 things that geographic data link together?
- geospatial: where (discrete location in space) (
- attributes: what (or descriptions of the place)
- Metadata: describes both geospatial and attribute data (data about data, ex. creation date)
What are characteristics of geographic data?
mappable
- location
- size
- shape
Classes
- discrete
- continuous
What is continuous data?
set of data that has values that can take on any value within a finite or infinite interval. Represents phenomena in which each location on the surface is a measure of the concentration level or its relationship from a fixed point in space or from an emitting source (often measured)
- ex. temp, precip, elevation
- has fields (each location in space has a value assigned to it)
- often stored in raster format
What is discrete data?
set of data that has values that are distinct, separate, and have finite boundaries and identities (often counted)
- ex. houses
- identifiable units that have some sort of spatial reference
- usually stored in vector format
What is a point?
- a zero-dimensional object and has only the property of location
- has no area or length
- ex. can be used to represent a telephone
What is a line?
- A one-dimensional object that has the property of length
- ex. can be used to represent roads
- starts with a node, can have more vertices, and ends in a node
- has a direction
What is a polygon
- a two-dimensional object with properties of: area and perimeter
-made up of one or more lines that close in on themselves - ex. can represent a lake
What is topology?
It is the science and math of relationships used to validate the geometry of vector entities and for operations
- represents the spatial relationships between connecting or adjacent features in geospatial data
What are the 3 features of vector topology
- adjacency: how one polygon relates to another polygon, (when sharing a common boundary)
- connectivity: how lines can intersect with one another
- containment: how locations are situated inside of a polygon boundary
Why is topology helpful?
- helps with searching adjacency relationships in large datasets
- allows for analysis (ex. which countries border Switzerland)
What occurs when the geographic space of an object is distorted (ex. projecting)?
- geometrical relationships change (metric)
- topological relationships remain constant (non-metric)
How does raster data work?
- define space as an array of equally sized cells arranged in rows and columns. Each cell contains an attribute value and location coordinates
What kind of attribute values can be held in raster cells?
- Binary (1 or 0)
- Categories (usually stored as integer numbers)
- integer of float (numbers with decimals)
