Objects And Fields

Question 1

What are Discrete objects

Answer 1

Objects + spatial footprints = features

Points lines and areas (or volumes) having known properties

Question 2

Characteristics of objects

Answer 2

Objects can be manipulated and edited
Objects can be found in the real world
Objects may overlap
Objects can be counted

Question 3

Characteristics of fields

Answer 3

Things it’s worth measuring at almost every location on the planet
Fields contain variables that have one value everywhere
The value of the variable is a function of time and space
Field is a way of conceiving geography as a set of variables each having one value at every location on the planet

Question 4

What does a geo-atom look like

Question 5

What features represent variables?

Answer 5

Polygons
Grids
TIN
Sample points
Contours

Question 6

What are the characteristics of representations of variables?

Answer 6

Entities is property of the representation, not the phenomenon
Cannot be manipulated
Cannot overlap

Question 7

How does the conceptual model influence the data model

Answer 7

Given I conceptualise the lake as an object I use a vector model

Given I conceptualise the lake as a field I use a raster data model

Question 8

What does the best representation depend on?

Answer 8

Application area (e.g. orientation)
Supported operations (e.g. area)
Costs (centroid vs polygons)
Scale (cities as points)

Question 9

What is the difference between models and rendering?

Answer 9

Conceptual models decide what representation we want, in this case objects
The data model is the type of representation, the this is a line

Representation renders at a certain width if matches certain characteristics

Question 10

What is a cell?

Answer 10

A cell is the smallest distinguishable unit.

The better resolution the more information can be stored

Question 11

How does topology help with constraint checking

Answer 11

Topology defined in the domain (housing can’t go into someone else’s land) therefore would be a digitised error

Question 12

How do you store topology?

Answer 12

Points - point ID
Lines - begin in node and end node
Polygons - lines constituting a polygon ID

Question 13

What is a tesselation?

Answer 13

tesselations is an exhaustive regular it irregular partitioning of space with no gaps or overlaps in most cases square cells of raster data and also other alternative classifications of tester data

Question 14

Limitations of raster data

Answer 14

Winner takes all
KO-criterion

Requires a decision may change the interpretation

Question 15

How to convert raster to run-length codes

Answer 15

9 9 6 6 6 6 6 7
6 6 6 6 6 6 6 6 
9 9 6 6 6 6 7 7
9 8 9 6 6 7 7 5
 Goes to
2:9, 5:6, 1:7
8:6
2:9, 4:6, 2:7
1:9, 1:8, 1:9, 2:6,2:7, 1:5

Question 16

What are the issues with data compression

Answer 16

Data compression can dramatically reduce the amount of storage required to save data but at the same time increases processing costs

Question 17

What is quadree compression?

Answer 17

Only store information at higher resolution that is necessary

In raster that is the smaller cells, in the data model the node is split further

Question 18

What are the two main algorithms that convert vector to raster

Answer 18

Any cell rule - continuous but wider line

Near cell rule - thin line but may be discintinuous

Question 19

How to convert from raster to vector

Answer 19

Raster to cell Center points to smoothed lines

- post processing required e.g to smooth line

Question 20

Object data model

Answer 20

Owner has a relation to the parcel contained in a county

Question 21

Which is the best data model?

Answer 21

Vector models produce small data sets
Topological relations are handled using vectors
Analysis is simpler on raster data in many cases
Overlays are simple in the raster model
TINs provide flexible facet size
Object models include relations and Hierarchies