Week5: 12 Spatial Queries

Question 1

Containment query

Answer 1

Given a spatial object O, find all objects in the map that completely contain O
- when O is a point, the query is called point query (point-in-polygon or point location)

Question 2

Region Query

Answer 2

Given a region R, find all objects in the map that intersect R
- when R is a rectangle, the query is called ‘Window Query’

Question 3

Enclosure Query

Answer 3

Given a region R, find all objects in the map that are completely contained in R

Question 4

Clipping

Answer 4

Given a region R, extract all portions of objects in the map that are contained in R

Question 5

Line Intersection Query

Answer 5

Given a line L, extract all object in the map that intersect L

Question 6

Adjacency Query

Answer 6

Given an object O, extract all objects in the map that are adjacent to O i.e. share a bounding entity

Question 7

Metric Queries

Answer 7

relate to distance. Given two objects, how far apart are they?
- Proximity query

Question 8

Nearest Neighbour Query

Answer 8

Given an object O, find the object in the map that is closest to O
- typically for points

Question 9

Range Query

Answer 9

Given an object O, find all objects in the map that are within a given distance d from O
- typically for points

Question 10

Spatial join

Answer 10

Given two sets of spatial objects S & S’, find all pairs (O,O’) of objects such that O e S & O’ e S’, O n O’ not null
- Spatial predicates other than intersection are also possible e.g. all pairs of objects that are within a given distance from each other

Question 11

Map Overlay

Answer 11

Given two maps, M & M’, return a third map that contains objects from M & M’ and new objects whose geometry corresponds to the intersection of objects belonging to M & M’

Question 12

Merge Query/Operation

Answer 12

Given two or more objects, O & O’, return their geometric union
- this operation is used in map generalisation to perform object aggregation

Question 13

Spatial Queries involve ..

Answer 13

the geometry of objects and their spatial relations (in particular topological queries are based on topological properties)
Therefore, it is important to have data structures that support efficient computation of geometric properties and spatial relations

Question 14

GIS query

Answer 14

1) What state contains city A

2) What states are crossed by river B

Question 15

Geometric query

Answer 15

1) What polygon in the plane subdivision contains point A?

2) What polygons in the plane subdivision are intersected by polyline B

Question 16

Other spatial queries e.g. clipping make extensive use of ….

Answer 16

line intersection algorithms that have been proposed in the field of computational geometry