Copyright, © Qiming Zhou GEOG3600. Geographical Information Systems Geographical Query

2  What is geographical query?  Queries and reasoning  Measurements

Geographical Query3 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 Query4 Queries and reasoning  Selective map display  Spatial query  Attribute query  Spatial relationship query  Advanced SQL query

Geographical Query5  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 Query6 Selective map display (1)

Geographical Query7 Selective map display (2)

Geographical Query8 Selective map display (3)

Geographical Query9 Selective map display (4)

Geographical Query10 Selective map display (5)

Geographical Query11 Selective map display (6)

Geographical Query12 Spatial query - point

Geographical Query13 Spatial query - line

Geographical Query14 Spatial query - area

Geographical Query15 Spatial query with background

Geographical Query16 Spatial query with ‘links’

Geographical Query17 Attribute query

Geographical Query18 Attribute query

Geographical Query19 Spatial relationship query

Geographical Query20 Extended SQL query

Geographical Query21 Measurements  Distance and length  Area  Shape

Geographical Query22 Distance and length (x 1, y 1 ) (x 2, y 2 ) 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 Query23 Shape of an area Measure the shape of zones in terms of their proximity to a perfect circular shape For each zone in X measure the area of the zone (C) measure the perimeter of the zone (P) Circle U = 1 Any other shape 0 < U < 1

Geographical Query24 Continents and islands Determine 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 Query25 The Euler number An 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 X count a count b U = a - b where a = number of enclosed islands b = number of islands which make up the region itself A B For A: a = 0; b = 5; U = -5 For B: a = 3; b = 1; U = 2

Geographical Query26 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.