where’s my data?

COLIN MACKAY

WHERE’S MY DATA?

Spatial queries in SQL Server 2008

SQL Bits III – 13th September 2008

HTTP://WWW.COLINMACKAY.NET

WHAT’S COVERED IN THIS TALK New data types geometry and

geography Spatial references Spatial operations Spatial indexes Case study

WHY SHOULD I CARE ABOUT SPATIAL DATA?

80-90% of all data has a spatial element Where are your customers? Where are your assets? Where are potential customers? Where are the flood risks? Where are your complaints coming

from? Where are the accident black-spots? Where are crimes happening?

COULD FUDGE THE QUERIES Postcodes in

Glasgow Zoned Historical reasons G5 adjacent to G42 G40 in an island Postcodes

designed for delivering letters

WHAT DOES SQL SERVER 2008 PROVIDE? The data analysis engine No useful rendering engine

Virtual Earth Map Point Other GIS systems

OGC Standards compliance Plus some “extension” methods of their

GEOMETRY X/Y coordinate on a

planar grid British National Grid Works well to

~750,000km2 Different projections

GEOGRAPHY Geodetic

coordinates Covers larger areas International

datasets Approximation

Earth actually flattened sphere (oblate spheroid)

Different models Airy 1830 (used by

OS) WGS84 (used by

SRID Spatial Reference Identifier All spatial data has an SRID SRIDs must match for spatial

operations Null returned if SRIDs don’t match

Geometry can have an SRID of 0 Not Geography.

TYPES OF SPATIAL DATA Point LineString Polygon GeomCollection MultiPolygon MultiLineString MultiPoint

From BOL

COLIN MACKAY

colin@scottishdevelopers.com

http://www.colinmackay.net

CREATE POINT DATA

FINDING DISTANCESSELECT a.Name AS StartVenue, b.Name AS EndVenue, a.Location.STDistance(b.Location) / 1000.0 As DistanceFROM Venue AS aINNER JOIN Venue AS b ON a.Id < b.IdORDER BY a.Id, b.Id

GCU 60Dundee U

62 102

MS TVP 520 537 572MS Edin’

6 66 58 521

HBOS GCU Dundee U

MS TVP

LINESTRING A linestring is a series of coordinates 1 dimension Defines a linear object

Road Railway line River

CREATING LINESTRINGS Can use

STGeomFromText STGeomFromWKB STLineFromText STLineFromWKB Parse

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CREATE LINESTRING DATA

GEOMETRY LENGTHS & DISTANCES Geography uses SI Units Geometry uses the units of the planar

system

The square of the hypotenuse is equal to the sum of the square of the other two sides

Not to scale

3 units

4 units

? unitsDistance from A to B:√(32+42) = 5

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INTERSECTING LINES

POLYGON A series of coordinates in a closed ring

First and last coordinate are the same 2 dimensions Defines an area

GEOGRAPHY POLYGON ORIENTATION Interior is

everything inside an anti-clockwise ring Everything on the

left-hand side of the perimeter line.

GEOGRAPHY POLYGON ORIENTATIONThe specified input does not represent a valid geography instance because it exceeds a single hemisphere. Each geography instance must fit inside a single hemisphere. A common reason for this error is that a polygon has the wrong ring orientation.

CREATING POLYGONS Can use

STGeomFromText STGeomFromWKB STPolygonFromText STPolygonFromWKB Parse

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CREATING POLYGONS

FICTIONAL CASE STUDY Estate Agent

Filter by price, # bedrooms, type – EASY! Filter by location?

Until now very vague

COMMON SPATIAL QUESTIONS

Near a railwa

y statio

Near my work

Near a motorway junctionNear a good

school Inside the cityOutside the city

THE DATA Railway data

Stations Routes

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SIMPLE SPATIAL QUERIES

DOESN’T ALWAYS WORK Edinburgh - Glenrothes

(via Kirkcaldy)Name DistKM-------------------------- ----------------Edinburgh Waverley Station 0Haymarket 1.89298770395887South Gyle 6.95446540329848Burntisland 12.086984317701Dalmeny 12.49585147351Kinghorn 13.1439998546632Aberdour 13.3392361220632North Queensferry 14.3833962761344Dalgety Bay 15.0082794626365Inverkeithing 15.7316327831032Kirkcaldy 17.9484646860063Glenrothes With Thornton 23.7022936117453

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LOOKING FOR A HOME

DISPLAY THE PROPERTIES

SPATIAL INDEXING Decomposes space

into 4 levels of grid Level 1 is the top Cells are uniform in

a level A level can be a

4x4, 8x8 or 16x16 grid 8x8 by default

RESTRICTIONS Table must have a primary key Primary key cannot subsequently be

changed. Not on views Maximum of 249 Spatial indexes per

column

WHY HAVE MULTIPLE INDEXES ON ONE COLUMN

Where geometry/ geography sizes vary

e.g. Rail routes Small: Suburban

lines Large: Intercity lines

SPATIAL INDEXING Supports

STIntersects STEquals STDistance

One Geography must be a point Both sides of the spatial operation must

have the same SRID

SPATIAL INDEXING ON A GEOMETRY Must specify boundary of spatial area Additional methods supported

STContains STOverlaps STTouches STWithin

AND THERE’S MORE! CodePlex project

More spatial methods Aggregations Scripts

http://www.codeplex.com/sqlspatialtools

WHAT I’VE NOT MENTIONED GML

Import and export M and Z

Can store Cannot operate.

Other spatial Operations Geometry has more!

Visualisation .NET application

integration Data Importing

GET MORE INFORMATION Slide Deck on my website

http://www.colinmackay.net Blog posts on Spatial Data

http://blog.colinmackay.net

QUESTIONS

where’s my data?

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