Lecture #3 Flashcards
Describe Topology and how it relates to GIS
Topology is spatial relationships in the data represntation of features and phenomena in the world and how those geometric representation relate logically. A GIS only understands the topology if you provide it with it
What is digitization?
The process of converting analogue data to digital using methods such as scanning or a digitizing tablet
What are some problems with scanning?
Text may show up as a feature, contour lines may be broken with text, special symbols get lost and automatic feature recognition isn’t that accurate
What is the sliver error?
An digitizing error where there is dead space between polygons
What is the line closing error?
A digitizing error where lines don’t extend far enough or too far
What are buffers?
Area around a feature with a set radius
What is the Euclidean and Manhattan distance?
The Euclidean distance is the distance between two points directly while the Manhattan distance is the distance following intersecting lines
What are layer-on-layer operations?
Layer-on-layer operations are operations that are performed by using one layer to affect another layer
What are models and what types do we see?
Models are how we imagine geographic space. We see Vector, Raster and Object
What is the difference between a vector and raster model?
Vector models show unique features that don’t exist everywhere and don’t show empty space
Raster models estimate based of the average of each grid
What do we call the process of rastering data?
Tessillation
What is structure?
How we store data in a computer
what are the spatial database models?
Hierarchal, network and relationship. These show lines, polygons and points
What is a hierarchal database structure?
It is treelike. The features can be repeated and the polygons are at the top while the points are at the bottom
What is a network data structure?
Uses pointers and everything can only appear once. It uses less storage and represents the same thing
What is a relationship data structure?
A spreadsheet containing data, row (records) and columns (fields) contain data and relations between datasets are noted and a common dataset is created / found
What are spatial questions we want to answer?
LIPTC (location, implications, patterns, trends, conditions)
What is an entity?
An individual point on a GIS
What is an attribute?
data about the entity
What is a feature?
An object in the real world implemented into a GIS
What is a data layer?
a data set for the area of interest in a GIS
What is an image?
A data layer in a raster array
What is a cell?
individual cell of a raster representation
What is a function or operation?
a data analysis performed by a GIS
what is an algorithm?
The computer sequence implementation
What are some vector operations?
Boolean overlay, geometric composites, layer-on-layer selection, buffers, Euclidean distance, Manhattan distance
What are vector operations?
Measurement techniques using coordinates, analysis
What are attribute queries?
Looking at characteristics of features
What are spatial queries?
Attribute queries in a location
What are boolean operations?
Overlapping geometry of features layer by layers
Boolean algebra is used to determine inclusion, exclusion, intersection and union
Think about venn diagrams
Combined area of the same thing (A.OR.B) (UNION)
Combined area of two different things (A.AND.B) (INTERSECT)
Combined area where A overlaps B (B.NOT.A) (CLIP)
What is a union?
Combined area of the same thing (A.OR.B) (UNION)
What is an intersect?
Combined area of two different things (A.AND.B) (INTERSECT)
What is a clip?
Combined area where A overlaps B (B.NOT.A) (CLIP)
Describe proximity
Selecting features near a line
Containments contains
Line-on-polygon selection
Point-on-polygon selection
Overlap contains
Polygon-on-line selection
Polygon-on-point selection
Polygon-on-polygon selection
What is dissolving in topological overlay?
Removes borders of overlapping polygons or creates a new polygon
What is a clip in topological overlay?
Only the input layer features show and overlap the original layer
What is a generating globe?
The stage after the ellipsoid but before the map
What are the three main map projections?
Planar, conic and cylindrical
Generalization is
making data less detailed (think coastline)
Abstraction is
Only looking at relevant data of something
