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