GIS Section 1 Flashcards
Studying for Intro to GIS Midterm!
What is a GIS?
An information system applied to geographic data, 2 main definitions:
- use geographically-referenced data to carry out operations for spatial analysis
- system of hardware, software, and procedures to support input, storage, retrieval, and display of geogrpahically-referenced data
What is the main purpose of GIS?
support DECISION-MAKING related to spatially-distributed entities
What are some benefits of using GIS?
- consistent framework for spatial analysis
- can make connections between activities
- allows accessing admin records via their geographic position
Name some disciplines that contribute to GIS
cartography, surveying, statistics, computer science, mathematics (geometry), civil engineering, agronomy, ecology
Aside from hardware/software, what else goes into a GIS?
approaches/methods for data analysis, people and their knowledge!
What is the starting point for a good GIS?
user needs analysis
(identify what questions the GIS will be answering!)
What are the 3 main hardware components of a GIS?
- input module
- CPU
- output module
What is a subsystem?
collections of dedicated hardware and software for accomplishing the main tasks of GIS (input and queries)
What are the main modules in a GIS?
- input module
- storage/database module
- display/reporting module
- data processing/transformation module
What is a DBMS?
Database Management System
(central control of data management – both spatial and attribute data, as well as topological rules)
What does the Retrieval and Transformation subsystem do?
retrieval - connects to output/display data
transformation - for maintenance (update and edit) or data analysis
What does the display and output subsystem module do?
prepare data for output via Output Module
Through which 3 modes can we view the world?
- spatial
- temporal
- thematic (theme whose spatial variability = observed/measured)
(in practice, fix one mode (time), vary a second (space), and observe the third (theme))
What is ASCII?
American Standard Code for Informatino Interchange
contains characters used as text in categorical attributes (names)
What are the 6 data types?
- binary
- byte
- integer
- real
- date
-ASCII
(also packed binary but whatever)
What is the range of integer and real data etc.?
Integer: -32768 to 32768
(65,536 possible values)
Real: real numbers to 7 decimal places (3.4*10^38)
Bytes: 0-255
How many bits to store integers and reals(floating point)?
Integers: 32 bits
Reals: 128 bits
What are the two elements of efficient file storage?
rapid access and rapid cross-referencing!
What are the 3 components of spatial data?
- spatial objects
- attributes
- topology
What is a graphic primitive?
used to digitally represent real objects
What are the basic 1-dimensional object types?
point, node
What are the 7 basic types of 1-dimensional objects?
- line segment
- string
- arcs
- ring (of strings)
- ring (of arcs)
- link (between two nodes)
- directed link
What are the 4 basic 2-dimensional object types?
simple polygon
- complex polygon
- interior area
- picture element
In rasters, what is the relationship between resolution and cell dimension?
high resolution = low cell dimension (small pixels)
In what sequence are raster files read?
from top left corner
What is pixel resolution?
the minimum linear dimension of the smallest unit of geographic space for which data are recorded
What types of resolution affect how a map is read?
- printer resolution
- monitor resolution
- actual map/data resolution
What are the steps in creating a raster image?
- decide on level of resolution
- overlay regular grid on source map
- code each cell with an appropriate value
- input values in a text (ASCII) file
What are the three methods for creating a raster image?
- cell-by-cell entry
- import from digital image source
- import from scanned devices (paper maps)
What 3 shapes are real-world entities abstracted into?
- points (nodes)
- lines (arcs)
- areas/polygons
What is the unique name of a feature?
Primary Key
How are vector data (points, lines, polygons) stored?
points: single X,Y coordinate pair
Lines: string of X,Y pairs
Polygons: Closed loop of X,Y pairs (first and last are the same)
What are the 2 storage approaches for vector data?
- polygon storage approach (problem of shared boundaries)
- arc storage approach (topology instead of shared boundary)
What is planar enforcement?
the set of coded rules that objects must follow to build topology correctly (ex. two 1-D objects must not cross)
What is the relationship between digitizing and editing?
poor digitizing –> large need for editing
What is topology?
branch of geometry that deals with properties of features that are unchanging and depend on context (important in defining spatial relationships between objects)
What are feature classes?
Features with the same type of geometry – ie. any grouping of points, lines, or polygons
- feature classes have attributes stored in tables
What are shapefiles?
vector files for storing location/attribute data of points/lines/polygons
- accompanied by 2 other files (3 total)
- SHP (geometry), SHX (indexing of feature geometry), DBF (database file as attribute table)
What is a GCM?
Global Climate Model/General Circulation Model
- practical example of raster data
- useful in projecting climate change
What physical processes can a GCM represent?
- motion
- thermodynamic energy
- water vapour mass continuity
How do GCMs differ (from each other)?
- different grid approaches
- different numerical methods for solution
- vertical discretization
How does a GCM grid represent the Earth?
200x200km lateral and 10km vertical grid cells (ie. atmosphere divided into many 3-D cells)
What GCMs will have higher/lower resolutions?
higher resolution = local/regional GCMs
lower resolution = global GCMs
What resolution do typical Global Climate Models have?
grid of ~300km squares
