copyright, 1998-2012 © qiming zhou geog3600. geographical information systems geographical query

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Copyright, 1998-2012 © Qiming Zhou

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TPU-based Population Density0 - 1200012000 - 3520035200 - 5920059200 - 102400102400 - 193700

Distance Zones to Hospital123

Population Density0 - 1270012700 - 3690036900 - 6870068700 - 110700110700 - 193700

# Surveyed Hospitals

6 0 6 12 18 24 Kilometers

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Hong Kong Hospital Coverage

GEOG3600. Geographical Information Systems

Geographical Query

Geographical Query 2

Geographical Query

What is geographical query? Queries and reasoning Measurements

Geographical Query 3

What is geographical query? Geographical query is the most basic of

analysis operations. To answer simple questions posed by the user. No change occur in the database. No new data are produced.

The operations vary from simple to complex, well-defined queries.

Query and reasoning Measurements: simple numerical values that

describe aspects of geographical data.

Geographical Query 4

Queries and reasoning

Selective map display Spatial query Attribute query Spatial relationship query Advanced SQL query

Geographical Query 5

Selective map display Displays the locations or all objects using points and

arcs, with or without background. Attributes and entity types can be displayed by

varying colours line patterns and point symbols. Relational query

Different systems use different ways of formulating queries. Structured Query Language (SQL) is an attempt to provide a “standard” way in querying data base.

The user can select object interested and produce maps.

Selective map display

Geographical Query 6

Selective map display (1)

Geographical Query 7

Selective map display (2)

Geographical Query 8

Selective map display (3)

Geographical Query 9

Selective map display (4)

Geographical Query 10

Selective map display (5)

Geographical Query 11

Selective map display (6)

Geographical Query 12

Spatial query - point

Geographical Query 13

Spatial query - line

Geographical Query 14

Spatial query - area

Geographical Query 15

Spatial query with background

Geographical Query 16

Spatial query with ‘links’

Geographical Query 17

Attribute query

Geographical Query 18

Attribute query

Geographical Query 19

Spatial relationship query

Geographical Query 20

Extended SQL query

Geographical Query 21

Measurements

Distance and length Area Shape

Geographical Query 22

Distance and length(x1, y1)

(x2, y2) 2122

12 yyxxD

Computation of line length

The poly line representation of a smooth curve tends to be shorter.

The length of a path as travelled on Earth’s surface may be longer than its horizontal projection.

Geographical Query 23

Shape of an areaMeasure the shape of zones in terms of their proximity to a perfect circular shape

For each zone in Xmeasure the area of the zone (C)measure the perimeter of the zone (P)

C

Pconvexity

convexity

aU

CircleU = 1

54.322

2

R

R

C

Pconvexitya

circle

circlecircle

Any other shape0 < U < 1

Geographical Query 24

Continents and islandsDetermine the shape of region by analysing the number of enclosed islands and number of zones which make up the region itself. If the number of zones is greater than the number of enclosed islands, then the region is closer to the shape of “islands”. Otherwise, when the number of enclosed islands is greater than the number of zones, then the region is closer to the shape of “continents”.

Continents Islands

Geographical Query 25

The Euler numberAn area is closer to either a continent or island shape can be determined by it Euler number. The Euler number is calculated by subtract the number of islands which make up the region itself from the number of enclosed islands by that region. If the Euler number is greater than 0, the region is closer to a “continent”, while the Euler number is less than 0 then the region is closer to “islands”.

For each region in Xcount acount bU = a - b

where

a = number of enclosed islands

b = number of islands which make up the region itself

AB

For A:a = 0; b = 5; U = -5For B:a = 3; b = 1; U = 2

Geographical Query 26

Summary

Geographical query is the most frequently used operation in GIS.

Geographical query includes spatial, attribute and spatial relationship queries.

The purpose of geographical query is to retrieve geographical information from GIS based on user-defined criteria.

Spatial measurements can be made in GIS including distance, area and shapes.

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