GIS Flashcards
(25 cards)
Type of GIS software
ArcGIS, QGIS, GEOMEDIA (used by local govt), Smallworld (used by utility companies)
2 types of spatial features
Discrete (Roads, houses, wells) —> Vector
Continuous (Rainfall, elevation) —> Raster
Discrete Geographic Features are better represent by what?
Georelational Vector Data Model (points, lines, polygons)
What are the basic graphical elements of the vector data model
A point, a line, an area
Basic rules with vector data
Each thematic object forms its own layer e.g. roads and railways are separate layers
Each layer can only have 1 type of feature (can’t mix points with polygons)
Continuous Geographic Features are better represented by
Raster Data Model (grids and cells)
An example of Raster Data Model
A digital elevation model (dem) is a digital terrain representation technique, where elevation values/topography are stored in raster cells. A DEM is very useful for hydrological modeling
Other forms of Raster Data Models
Aerial photographs (Digital Orthophoto Quadrangle)
Satellite images
What is the range of pixel values in a raster image and what do they represent
Between 0 - 255 representing the brightness of that cell
0: dark cell
255: bright cell
How can remote sensing be used in GIS
Can be used to collect information about objects on the ground using Satellite or Plane based sensors
A form of primary data collection
Why does vegetation reflects near IR
Because they’re really absorbing red, green and blue to convert into food, so IR is all that’s left over
How can the number values be converted into a map with raster
Colors are a proxy for the number values
What are the 2 types of analysis with GIS
Vector and Raster analysis
What are types of vector analysis
Buffers, Overlays (union, clip, intersection), Network analysis (shortest path), location-allocation, spatial statistics
What are types of Raster analysis?
Map algebra, DEM-specific, Time-series
What is a buffer?
Polygons created by reclassification at a specified distance from point, line, area
What is an overlay?
Most powerful feature of modern GIS
Place one “theme” (e.g. soils) over another (e.g. proposed parking lot) and check for soils which will cause problems of drainage for proposed parking lot (spatial correlation)
Another definition: the geometric intersection of multiple datasets to combine, erase, modify, or update features in a new output dataset
How can I use buffers and overlays in GIS analysis?
Buffers can be combined with polygons overlays in order to analyze spatial information
e.g. Find all habitat areas of owls that are within 500 meters of country roads
Is bird flu ecoregion based
Yes, 25 ecoregions (representing 8% of terrestrial surface area) accounted for 77% of cases
What kind of information can vector data have?
Attribute information, which tells the database server what options, or attributes, to assign to the smart large object
What is query attribute
The Query Attribute check identifies errors based on Structured Query Language query that can include one or more attribute values. Features or rows returned by the query are written as an error.
Attribute queries in QGIS
One method to select features in a layer is to select features using an attribute query:
- Right click on the layer’s name on the Layer Panel
- Select Query from the
Why are map projections complicated
It is difficult to to correctly express a 3D sphere in 2D
Coordinate Systems
Coordinate systems - (x,y) coordinate systems for drawn through the center of the projection creates a new reference (x,y) for places in the globe. Map we know: Universal Transverse Mercator
