GIS Section 1

Question 1

What is a GIS?

Answer 1

An information system applied to geographic data, 2 main definitions:

1. use geographically-referenced data to carry out operations for spatial analysis
2. system of hardware, software, and procedures to support input, storage, retrieval, and display of geogrpahically-referenced data

Question 2

What is the main purpose of GIS?

Answer 2

support DECISION-MAKING related to spatially-distributed entities

Question 3

What are some benefits of using GIS?

Answer 3

• consistent framework for spatial analysis
• can make connections between activities
• allows accessing admin records via their geographic position

Question 4

Name some disciplines that contribute to GIS

Answer 4

cartography, surveying, statistics, computer science, mathematics (geometry), civil engineering, agronomy, ecology

Question 5

Aside from hardware/software, what else goes into a GIS?

Answer 5

approaches/methods for data analysis, people and their knowledge!

Question 6

What is the starting point for a good GIS?

Answer 6

user needs analysis
(identify what questions the GIS will be answering!)

Question 7

What are the 3 main hardware components of a GIS?

Answer 7

• input module
• CPU
• output module

Question 8

What is a subsystem?

Answer 8

collections of dedicated hardware and software for accomplishing the main tasks of GIS (input and queries)

Question 9

What are the main modules in a GIS?

Answer 9

• input module
• storage/database module
• display/reporting module
• data processing/transformation module

Question 10

What is a DBMS?

Answer 10

Database Management System
(central control of data management – both spatial and attribute data, as well as topological rules)

Question 11

What does the Retrieval and Transformation subsystem do?

Answer 11

retrieval - connects to output/display data

transformation - for maintenance (update and edit) or data analysis

Question 12

What does the display and output subsystem module do?

Answer 12

prepare data for output via Output Module

Question 13

Through which 3 modes can we view the world?

Answer 13

• spatial
• temporal
• thematic (theme whose spatial variability = observed/measured)

(in practice, fix one mode (time), vary a second (space), and observe the third (theme))

Question 14

What is ASCII?

Answer 14

American Standard Code for Informatino Interchange

contains characters used as text in categorical attributes (names)

Question 15

What are the 6 data types?

Answer 15

• binary
• byte
• integer
• real
• date
  -ASCII

(also packed binary but whatever)

Question 16

What is the range of integer and real data etc.?

Answer 16

Integer: -32768 to 32768
(65,536 possible values)

Real: real numbers to 7 decimal places (3.4*10^38)

Bytes: 0-255

Question 17

How many bits to store integers and reals(floating point)?

Answer 17

Integers: 32 bits

Reals: 128 bits

Question 18

What are the two elements of efficient file storage?

Answer 18

rapid access and rapid cross-referencing!

Question 19

What are the 3 components of spatial data?

Answer 19

• spatial objects
• attributes
• topology

Question 20

What is a graphic primitive?

Answer 20

used to digitally represent real objects

Question 21

What are the basic 1-dimensional object types?

Answer 21

point, node

Question 22

What are the 7 basic types of 1-dimensional objects?

Answer 22

• line segment
• string
• arcs
• ring (of strings)
• ring (of arcs)
• link (between two nodes)
• directed link

Question 23

What are the 4 basic 2-dimensional object types?

Answer 23

simple polygon
- complex polygon
- interior area
- picture element

Question 24

In rasters, what is the relationship between resolution and cell dimension?

Answer 24

high resolution = low cell dimension (small pixels)

Question 25

In what sequence are raster files read?

Answer 25

from top left corner

Question 26

What is pixel resolution?

Answer 26

the minimum linear dimension of the smallest unit of geographic space for which data are recorded

Question 27

What types of resolution affect how a map is read?

Answer 27

- printer resolution - monitor resolution - actual map/data resolution

Question 28

What are the steps in creating a raster image?

Answer 28

1. decide on level of resolution 2. overlay regular grid on source map 3. code each cell with an appropriate value 4. input values in a text (ASCII) file

Question 29

What are the three methods for creating a raster image?

Answer 29

- cell-by-cell entry - import from digital image source - import from scanned devices (paper maps)

Question 30

What 3 shapes are real-world entities abstracted into?

Answer 30

- points (nodes) - lines (arcs) - areas/polygons

Question 31

What is the unique name of a feature?

Answer 31

Primary Key

Question 32

How are vector data (points, lines, polygons) stored?

Answer 32

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)

Question 33

What are the 2 storage approaches for vector data?

Answer 33

- polygon storage approach (problem of shared boundaries) - arc storage approach (topology instead of shared boundary)

Question 34

What is planar enforcement?

Answer 34

the set of coded rules that objects must follow to build topology correctly (ex. two 1-D objects must not cross)

Question 35

What is the relationship between digitizing and editing?

Answer 35

poor digitizing --> large need for editing

Question 36

What is topology?

Answer 36

branch of geometry that deals with properties of features that are unchanging and depend on context (important in defining spatial relationships between objects)

Question 37

What are feature classes?

Answer 37

Features with the same type of geometry -- ie. any grouping of points, lines, or polygons - feature classes have attributes stored in tables

Question 38

What are shapefiles?

Answer 38

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)

Question 39

What is a GCM?

Answer 39

Global Climate Model/General Circulation Model - practical example of raster data - useful in projecting climate change

Question 40

What physical processes can a GCM represent?

Answer 40

- motion - thermodynamic energy - water vapour mass continuity

Question 41

How do GCMs differ (from each other)?

Answer 41

- different grid approaches - different numerical methods for solution - vertical discretization

Question 42

How does a GCM grid represent the Earth?

Answer 42

200x200km lateral and 10km vertical grid cells (ie. atmosphere divided into many 3-D cells)

Question 43

What GCMs will have higher/lower resolutions?

Answer 43

higher resolution = local/regional GCMs lower resolution = global GCMs

Question 44

What resolution do typical Global Climate Models have?

Answer 44

grid of ~300km squares