11: Vector I

Question 1

LINE GENERALISATION

Answer 1

reduction of level of detail in data as to gain clarity in information

• reduce data noise, enhance relevant patterns
• reduce volume of data without adversely affecting its use
• make things as simple as possible but not simpler (Albert Einstein)

Question 2

SPATIAL QUERIES

Answer 2

simples operational capabilities of any GIS

immediate answer to a map/database query:

• how many X are within Ykm of this point?
• which is the closest X to Y?

Two typical types of GIS queries:

• spatial queries by geometry
• spatial queries by data attribute selection

GIS can answer these questions because of geometry and topology

Question 3

BUFFERING

Answer 3

based on concept of proximity

separates a map into two areas:

1. within specified distance of selected map features
2. not within specified distance of selected map features

buffer zone - area within the specified distance

selected map features for buffering may be points, lines or polygons

Question 4

LIST MAP MANIPULATIONS

Answer 4

ways to manipulate each map layers
Clip
Eliminate
Split
Dissolve
Append

Question 5

POLYGON OVERLAY

Answer 5

layers can be combined to produce new layers through geometric intersections

find polygons formed by the intersection of two (or more) polygons

a layer produced by an overlay will contain both the spatial data and attribute data of the input layers

can overlay points, lines or polygons

Question 6

Spatial data query methods

Answer 6

Structured Query Language (SQL)

used to query the map layer
results can be mapped or presented in a conventional data table and / or directly in the map
useful to produce maps with subsets of the data (filters) or by theme/interest

Question 7

Spatial data query method

Answer 7

Structured Query Language (SQL)

code language used to query the map layer
results can be mapped or presented in a conventional data table and / or directly in the map
useful to produce maps with subsets of the data (filters) or by theme/interest

Question 8

Uses for buffering

Answer 8

sphere/zone of influence of a geographic object

zone of protection (which keeps undesirable geographic objects away from other objects)

Question 9

Clip

Answer 9

extracts input features contained within a clip feature

basically clip a study region to certain shape

Question 10

Clip

Answer 10

extracts input features contained within a clip feature

basically clip a study region to certain shape, doesn’t change the information inside

Question 11

Split

Answer 11

split layer into multiple new layers based on smaller areas/zones

not common to use

Question 12

Dissolve

Answer 12

aggregate smaller zonal units into larger zonal units based on a specific common attribute, type of generalisation

careful about spatial analysis due to modifiable unit problem

Question 13

Append

Answer 13

merge multiple map layers at edges into one bigger new layer

opposite of split

Question 14

Polygon overlay methods

Answer 14

if the input map has a different area extent that the overlay map, then the extent of the output may vary depending on the overlay method used

three common methods:
Union
Intersect
Identify

Question 15

Union overlay

Answer 15

preserves all map features from the input and the overlay maps

adding layers together with different extents, but retain all features of both

Question 16

Intersect overlay

Answer 16

intersect method preserves only the area common to the two input themes in the output

Question 17

Identity overlay

Answer 17

identity preserves only map features that fall within the area extent defined by the input map