Midterm review- spatial data models

Question 1

How does GIS store data?

Answer 1

In layers of discrete information.

Question 2

List the 3 steps of GIS representation

Answer 2

1. Selection of real world objects
2. representation in a standard way
3. quantification- computers store numeric values

Question 3

Explain the differences between fields and objects

Answer 3

Fields are continuous, no cut off point, i.e. elevation, temperature. no absolute zero
objects are discrete spatial entities and have identifiable boundaries. i.e. neighbourhoods, beaches.

Question 4

What are the 2 basic types of data?

Answer 4

spatial data and attribute data

Question 5

List the characteristics that define objects.

Answer 5

type (unique ID)
attributes (qualitative or quantitative data)
relations
geometry
quality

Question 6

List all the subsets of geometric and attribute data.

Answer 6

Geometric data: point, line, area

attribute data: qualitative data, quantitative data (ordinal, interval, ratio)

Question 7

What is digital orthophotography?

Answer 7

An aerial photo rectified to eliminate the effects of displacement so that its view always appears as though it is perpendicular to the ground.

Question 8

What is raster data model good for? Continuous fields or discrete objects?

Answer 8

Continuous fields.

Question 9

What information do you need for a raster model?

Answer 9

cell size, coordinate of the 4 corners.

Question 10

What are the three elements of a vector data mode used to represent the real world?

Answer 10

points,lines, and polygons.

Question 11

What are the 3 main data sources for raster data?

Answer 11

Satellite imagery
air photos
scanned maps

Question 12

What are nodes and vertices?

Answer 12

Line starts and ends with a special point called a node, and the rest of the points that make up a line are vertices.

Question 13

List 3 advantages and 3 disadvantages for Vector data model

Answer 13

-clean and easy to understand visuals
-accurate coordinate of data is maintained
-efficient operations regarding topology
but
-complex algorithms
-can’t represent continuous data
-spatial analysis within polygons is impossible

Question 14

list 3 advantages and 2 disadvantages of raster data model

Answer 14

-no geographic coordinates required except bottom left corner
-good for mathematical modelling and quantitative analysis
-integrates discrete and continuous data
BUT
-difficult to represent linear features
-most input data is in vector form. vector-raster conversion not good