Techniques for spatial data analysisanalysis

(Re)introduction to techniques for spatial data analysis

Last week• We thought about sources and types

(blunders systematic and random) errors(blunders, systematic and random) errors• We looked at using simple measures of error,

e.g. RMSE and CSE and their implications for e g S a d CS a d t e p cat o s oapplications in GIS

• We looked at the use of the Confusion Matrix d i f d li dto derive measures of data quality – and

hopefully some of you did the exercise…• We thought briefly about applications (e g• We thought briefly about applications (e.g.

navigation; census data) and their implications for data quality

Looking back…g• In GEO357 you looked at bear habitat

f t tifragmentation – Calculating landscape indices of fragmentation

Making maps of preferred bear habitat and reduced– Making maps of preferred bear habitat and reduced bear habitat

• You worked on a spatial analysis case study tooYou worked on a spatial analysis case study too• These are classic examples of Spatial Analysis• This semester we are going to spend most ofThis semester we are going to spend most of

our time looking holistically at Spatial Analysisthrough the following lectures…

Lecture topics…p• Today – (Re)introduction to techniques for spatial data

analysisanalysis• 02/04 Feb. – Polygon intersection• 09/11 Feb. – Spatial interpolation09/ e Spa a e po a o• 23/25 Feb. – Slope and aspect• 02/04 Mar. – Hydrological modelling functions• 09/11 Mar. – Viewsheds• 16/18 Mar. – Spatial data quality – Processing Errors• 23/25 Mar. – Multi-criteria evaluation – an example

M f h l di lMost of these relate directly to the labs…

Techniques for spatial data l ianalysis

• These learning objectives relate to the spatial analysis part of the course in particular:analysis part of the course in particular:– be able to explain what is meant by spatial analysis;– understand some of the different ways we can use y

spatial analysis;– understand how spatial operations may be

combined to perform complex analyses;combined to perform complex analyses;– know in detail how some specific operations work;– understand how to estimate and consider

t i t ( d th d t lit ) i ti luncertainty (and thus data quality) in spatial analysis; and

– be able to suggest and evaluate approaches to gg ppsolving specific problems using spatial analysis.

You all already know this…Two fundamentally different models of space andand properties in space: p p p

we can perceive space as being occupied by thingsp p g p y gwhich have a location and some attributes - these arecommonly known as entitiesORthe property of interest exists continuously through

d t b diff ti bl tspace and may or may not be differentiable at everypoint – commonly known as a field

For instance?

Some revision…

How might we model:g

Crevasses?Ice thickness?Albedo?Moraine position?

Entities or fields?

Franz Josef Glacier, New Zealand, 1956.

Entities or fields?

Vector or raster?, ,

What would be the attributes?

What data types would they

Unattributed photograph at the World Data Centre for Glaciology, Boulder.

What data types would they have?

Introduction to techniques for spatial data analysis

Wh t i ti l l i ( d h h ld ?)• What is spatial analysis (and why should we care?)• Some taxonomies1 (classifications) of operations– the

building blocks of analysisg y• Methodologies for spatial analysis – some different

ways of using spatial analysis• Examples – and questions about spatial analysis• Examples – and questions about spatial analysis

1 1. Classification, esp. in relation to its general laws or principles; that department of science or of a particular science or subject which consists in or relates toscience, or of a particular science or subject, which consists in or relates to classification; esp. the systematic classification of living organisms.

2. (With a and pl.) A classification of anything.

From www.oed.com (Oxford English Dictionary – very useful)

Today’s learning objectives…y g j

After today’s lecture, you will:• be able to give a number of definitions of

spatial analysis and illustrate each of these definitions with an example;definitions with an example;

• know what is meant by a taxonomy of operators for spatial analysis and you canoperators for spatial analysis, and you can give a detailed example of one; and

• understand how spatial analysis can be used• understand how spatial analysis can be used, in different ways, to explore or describe data.

What is spatial analysis?

The pump

Images from Tufte, E.R. 1997. Visual Explanations. A great book!

Some background

Snow was a genius –gthis graph shows howmany lives he saves…

So what does this graph show?

Y fi d d t il d

Images from Tufte, E.R. 1997. Visual Explanations.

You can find a detailed analysis of Snow’s workin Visual Explanations

Snow’s map (continued)Here is the same problem, but occurring p , gwhen we spatially aggregate with different unitsdifferent units… (MAUP)The pump

What other problems are there?

Being aware of these sort of problems with analysis is a key thing I would expect you to

Images from Monmonier, M. 1991. How to Lie with Maps, pp. 142-143.

g p yknow after this course…

Formal definitions“Spatial analysis is a set of methods whose results are not invariant under changes in the locations of the objects being analysed”j g yLongley et al. (Baby big book)

or more straightforwardlyor more straightforwardly

“Spatial analysis is a set of methods whose results change when the locations of the objects being analysedchange when the locations of the objects being analysed change”Longley et al., Goodchild

Goodchild asks “Is spatial analysis the ultimate objective of GIS?”

It is about asking questions…g q“To many it is query, and more especially analysis that are at the heart of GIS Query functions areare at the heart of GIS. … Query functions are concerned with inventory questions such as ‘Where is …’ Analysis functions deal with questions such as ‘What if

? ’ ”…?.’ ”Maguire and Dangermond, The Big Book

“…the GIS should be able to automate most of the geographic analyses that have developed over two and a half centuries of modern geographic thought ”half centuries of modern geographic thought.DeMers, Fundamentals of GIS

Oh dear…“One of the difficulties faced by GIS developers is due to the lack of consensus as to the methods needed for andthe lack of consensus as to the methods needed for, and the definition of, spatial analysis…”Bonham-Carter

“A good GIS will today probably contain over 1000 d ( th i i l t) b t f t i llcommands (or their equivalent) but few, typically none,

will be concerned with what might be correctly termed spatial analysis rather than data manipulation…”p y pOpenshaw (In the Big Book)

Where are we going?g g

• Definitions often help us discover what people thi k t h i di i li i b tthink a technique or discipline is about

• But, asking what is spatial analysis is a bit like asking what is geography?asking what is geography?

• The definition depends on who you are and what you do (it is situated to use the parlancewhat you do (it is situated to use the parlance of human geographers)

• One common statement about geography is• One common statement about geography is “Geography is what geographers do”

What do spatial analysts do?p y

• Perhaps we can define spatial analysis by l ki t l ?looking at some examples?

• We will do this in 3 ways:1 L k t t i f t f ti l1. Look at some taxonomies of operators for spatial

analysis (and GIS) 2. Look at some examples of the application of2. Look at some examples of the application of

spatial analysis to problems3. Examine the process of spatial analysis and see

if di id th d l i i t diff t lif we can divide methodologies into different classes

Burrough and McDonnell’s taxonomyg yClassify operations according to whether they work on:

Entities– Attribute operations– Distance/location operations

FieldsGive an non-exhaustive listincluding:

– Operations using built-in spatial topology

• All operations can result

g– Interpolation– Spatial filtering– Derivatives

in new attributes (attached to existing entities)

– Derivation of surface topology (drainage networks)

– Continuity assessment • Some operations can result in

new entities• This taxonomy is more useful

h h f ld

(clumping)– Non-linear dilation (spreading

with friction)h d h d d l f dthan their one on fields – Viewsheds, shaded relief and

irradiance

Albrecht’s 20 universal GIS operations

• Table 1. The 20 universal GIS operations

Created by analysing operations on a range of GIS and user interviews – published in Albrecht’s PhD thesis (grey literature) – note narrow definition of spatial analysis

Tomlin’s cartographic modelling

• An attempt to describe a language which formalises all the elements of raster overlay through a map algebra and four basic classes of operations

• Operations are:– local

f l

U = f( A, B, C )

– focal– zonal

globalWe must remember our scales of measurement here– global

• Perhaps overcomplicates in an attempt to simplify BUT a very useful classification

of measurement here…

simplify BUT a very useful classification…• Often applied to suitability analysis…

You have seen all this before…

• You must be able to do more than repeat it• You should be able to show you can discuss

and evaluate differing approaches… Y d b bl l h (b d• You need to be able to relate theory (based on the literature) to applicationsR b GIS i t GIS t !• Remember GIScience not GISystems!

Summarising…g• We have looked at some definitions of spatial

analysis and seen some arguments that say thereanalysis, and seen some arguments that say there are problems

• Looked at some taxonomies – one is based onLooked at some taxonomies one is based on conceptual model (entity vs. field), one the data model (raster) and one appears independent

• Together they appear to include most of the operations with which we are familiar in a GIS (which haven’t we seen?)(which haven t we seen?)

• Not any nearer to defining spatial analysis though…• Time for some examples!!• Time for some examples!!

Spatial analysis is what spatial analysts do?• Two case studies:

– BlowdownBlowdown is the blowing down of trees often over• Blowdown is the blowing down of trees, often over large areas by high winds

• Of interest for commercial reasons, and because large disturbances have important impacts on ecosystems (last from decades to centuries)

– Tranquillity analysisq y y• Finding tranquil places

• For each example we will try to summarise:– The main objective of the analysis– The data underlying the analysis

The operations carried out to make the analysis– The operations carried out to make the analysis– The approach taken in carrying out the analysis

Using GIS to analyse blowdowng y• Two papers:

Att ib t f bl d t h f i d– Attributes of blowdown patches from a severe wind event in the Southern Rocky Mountains, USA

– Using GIS to analyse a severe forest blowdown in theUsing GIS to analyse a severe forest blowdown in the Southern Rocky Mountains

• The first paper essentially sets out to describethe spatial pattern of blowdown patches with respect to attributes

• The second paper attempts to predict likelihood of blowdown with a range of variables using a sample dataset and verifyvariables using a sample dataset and verify model performance on the rest of the data

Blowdown descriptive paperp p p

• Blowdown patches were digitised from th tifi d t h t horthorectified stereo photographs

• Three classifications were made:P t h t i i bl d– Patches containing any blowdown

– Polygons with a percent down value attached– Because of errors in the above classification it was– Because of errors in the above classification, it was

reclassified (generalised) into 5 bands

• Attribute data were also collected to describe the forest (tree type, age, wetlands etc.)

• Detailed statistical analysis was undertaken yof the data

This shouldThis should make you very happy about howabout how much digitising you will have to do!!!(from Landscape Ecology)

More on blowdown 1• Analyses included:• Analyses included:

– Total percentage of blowdown by area– Mean and median size of patchesMean and median size of patches– Standard deviation of patch size– Patch Shape (measured using perimeter/area index

= 1.0 for a circle, infinity for an infinitely long narrow patch) – (c.f. looking at slivers next week)Comparisons of blowdown and non blowdown areas– Comparisons of blowdown and non-blowdown areas with appropriate statistical tests

– Comparison with harvested and fire-created patch properties

– Distance to other patches (important to organisms using the patches)using the patches)

More on blowdown 1

Blowdown paper 2• The second paper has a quite different

objective• It attempts to explain the occurrence of

blowdown through analysis and exploration of the dataof the data

• It does this through the following steps:1 A set of hypotheses about variables likely to cause1. A set of hypotheses about variables likely to cause

blowdown was formed – i.e.• Location of blowdown explained by variation in

wind (through sheltering)• Blowdown occurs where soil are moist and thin• Blowdown likely in areas where terrain is complex• Blowdown likely in areas where terrain is complex• Likelihood of blowdown greater at forest edges

(natural or anthropogenic)

More steps…p2. Variables describing these parameters are derived

e.g.g– Wind exposure through terrain and wind program– Terrain complexity through standard deviation in

moving windowmoving window– Forest and soil data reclassified and rasterised– Geology data manually digitisedgy y g– Road and utility maps used to find forest edges,

and buffered3 Sample data collected (paying attention to spatial3. Sample data collected (paying attention to spatial

autocorrelation)4. Variables significant in describing blowdown g g

extracted and logistic regression computed

Only a few more…y6. Model evaluated by comparing predictions to

rest of datasetrest of dataset7. Discussion and exploration of important

variables, key variables were topographic rather than vegetation, geology or soil exposure

Mapping tranquillitypp g q y• What is tranquillity?

“Tranquillity is primarily a natural resource. It reflects thedegree to which human beings experience the environmentdegree to which human beings experience the environmentunhindered by disruptive noise, movement and artificiallighting and structures. In a densely populated, heavilyg g y p p , ybuilt-up country like England it is scarce and its distributionis uneven.”

Background and aimsg

• This example is a real study carried out by the C i t P t t R l E l dCampaign to Protect Rural England

• The aims were to “develop ways of identifying, measuring and mapping tranquillity so thatmeasuring and mapping tranquillity so that it can be integrated fully into public policy decisions”decisions

• This is important because, in general, it is hard to include “feelings” in planning decisions…to include feelings in planning decisions…

www.cpre.org.uk

Basic methodologygy

• Initial pilot studies for small areas in the North f E l dof England

• Two key steps:S t t i h t t illit t l– Survey to ascertain what tranquillity means to people and factors that added or diminished it…

– Using basic Multi Criteria Evaluation techniquesUsing basic Multi Criteria Evaluation techniques they weighted factors and produced a “tranquillity map”

Finding out what tranquillity isg q y

• Carried out through participative research(i t i ti i k) t(interviews, questionnaires, group work) to study 4 key questions– What is tranquillity?– What is tranquillity?– What adds to it?– What is not tranquillity?What is not tranquillity?– What lessens it?

• Look at thresholds for intrusion on tranquillity q y(audible and visual) – when do things significantly disturb us?

Study area(s)

Pilot study (compared two areas)

Main study for all of England at 500mresolution

Results of tranquillity surveyq y yWhat tranquillity is – the top8 survey responses

What tranquillity is not – thetop 8 survey responses8 survey responses

1. Seeing a natural landscape2. Hearing birdsong3 H i d i t

top 8 survey responses1. Hearing constant noise from

cars, lorries and/or motorbikes2 Seeing lots of people3. Hearing peace and quiet

4. Seeing natural looking woodland

2. Seeing lots of people3. Seeing urban development4. Seeing overhead light pollution

5. Seeing the stars at night6. Seeing streams7. Seeing the sea

5. Hearing lots of people6. Seeing low flying aircraft7. Hearing low flying aircraftg

8. Hearing natural soundsg y g

8. Seeing power lines

W h t ti li th it iWe have to operationalise the criteria

Data

• Multiple datasets were used including– Land use data– Digital elevation models

Population centres– Population centres– Transport routes– Electrical transmission linesElectrical transmission lines– Wildlife surveys

• These were used to represent a total of 44 pdifferent factors used in the final model

Example - Perceived naturalnessp

Perceived naturalness based on survey results for different landcovers

g.. • Cell ends up with a

naturalness score

ntin

g

• Which is more natural – Prince’s

eme Island or Nose Hill?

• Mean value for a 3 3 i d i d

Impl 3x3 window is used

to take account of this…I

Opennessp

• Openness was considered to be associated with t illittranquillity

• One measure of openness is how much we can see from a pointsee from a point

• This was calculated with DEMs through calculating for every cell how many cells werecalculating for every cell how many cells were visible…

• We will return to the idea of visibility in the• We will return to the idea of visibility in the lecture on viewsheds…

Results

• Look at the map on th l ftthe left

• Which factors do you think are theyou think are the most important?

• Do you think all• Do you think all factors are independent of eachindependent of each other?

Source for the above examplespYou can find a short and detailed technical report( h ll th i f ) thi k t(where all the images came from) on this work at:• http://countryside-quality-

counts org uk/publications/2004-Tranquillity-Main-counts.org.uk/publications/2004 Tranquillity MainTechnical-Report.pdf (Detailed technical report on pilot study)

• http://www.cpre.org.uk/filegrab/saving-tranquilplaces-report.pdf?ref=2583 (Shorter report on main study)

Could we apply this model directly inCanada?Canada?

Exercise for next week• I would like you to think about a wilderness

d l f th C di R kimodel for the Canadian Rockies• Do a little reading about wilderness, and identify

some criteriasome criteria• These criteria should be from a Canadian (not a

British German or ?American?) perspectiveBritish, German, or ?American?) perspective…• How could these criteria be operationalised

and what data would be required?and what data would be required?

Three examples…p• The first example used analysis to efficiently

describe spatial patterns and relationshipsdescribe spatial patterns and relationships• The second tried to test hypotheses about

patterns and relationships in the data (but note patte s a d e at o s ps t e data (but otethat these hypotheses were actually formed after looking at the data)Th l d i l l i hi h ld b• The last used simple analysis which could be applied in spatial planning

• Openshaw suggests that these are the three• Openshaw suggests that these are the three contexts in which spatial analysis can be used (although he would argue with my examples)

So what is spatial analysis?p y

“The true value of GIS lies in their ability tol ti l d t i th t h i fanalyse spatial data using the techniques of

spatial analysis. Spatial analysis provides thevalue-added products from existing datasets”value added products from existing datasetsGoodchild, 1988

So perhaps spatial analysis is the process of goingfrom data to information where that gain in

l b hi d i h k i bvalue cannot be achieved without knowing aboutwhere things are and how they vary in space

Using spatial analysisg p y• Spatial analysis can be used to explore and describe

datadata• Depending on the application we may form

hypotheses and test them (though we need to understand spatial statistics esp. spatial autocorrelation)

• Many real world applications are heuristic1 we must• Many real-world applications are heuristic1 – we must make sure we tell people this

• Whichever approach we take we should consider the ppprocess of doing our spatial analysis

• Two contrasting approaches are presented here…

1 Serving to find out or discover (trial and error methodswhich we use in everyday life) from OED

A mechanistic approachpp

Input Store Manipulate DisplayAnalyseRetrieve

• Approach fits well with map production methodspp p p• Linear progression through groups of functions• Navigation straightforwardNavigation straightforward• Approach relatively inflexible

An exploratory approachCollect Resample

Input Store Manipulate ExploreRetrieve

ModelV if• Approach fits well with

Display

ModelVerify,refine

ppexperimental approach

• Problem orientated p y

• Exploritative, not definitive• Navigation involves multiple Which approach

li d i h f thg p

paths and feedback routes• Choice of functions relate to

applied in each of the three examples?

assumptions made

Summaryy• Spatial analysis is about asking questions,

exploring and describing dataexploring and describing data• There are lots of definitions – but it doesn’t

really matter exactly which one we chooseea y atte e act y c o e e c oose• It is important that we understand the nature of

the methodology we have chosen – are we i h h i (h ?) i h i i ?testing a hypothesis (how?) or using heuristics?

• Do we want to describe or explore the data?Y h ld thi k b t h t ill d i th• You should think about what you will do in the labs in relation to this lecture…

And don’t forget…g“Objects in a vector GIS may be counted, moved about stacked coloured labelled cut split slicedabout, stacked, coloured, labelled, cut, split, sliced, stuck together, viewed from different angles, shades, inflated, shrunk, stored and retrieved, and , , , ,in general, handled like a variety of everyday solid objects that bear no particular relationship to geography ”geography.”(Coucelis, 1992)

(And that goes for rasters too…)

References• Burrough and McDonnell.

1998. Principles of GIS• DeMeers.1997. Fundamentals

of GIS• The Big Book (Useful chapters

in both editions – particularly Openshaw, Developing Appropriate Spatial Analysis

• Longley et. al. 2001. GI Systems and Science

• Lindemann, J.D and Baker, W L 2002 U i GIS tAppropriate Spatial Analysis

methods for GIS) (Note this is online)

• Chrisman. 1997. Exploring GIS

W.L. 2002. Using GIS to analyse a severe forest blowdown in the S. Rocky Mtns. IJGIS, 16, 4, 377-400.Chrisman. 1997. Exploring GIS

• Albrecht et. al. 1997. VGIS: a GIS shell for the conceptual design of environmental

d l ( d )

Mtns. IJGIS, 16, 4, 377 400.• Lindemann, J.D and Baker,

W.L. Attributes of blowdown patches… Landscape Ecology

3 3 32models. In (ed. Kemp) Innovations in GIS 4.

16, 313-325.• Tomlin. 1990. GIS and

cartographic modelling.

Big Book material: http://www.wiley.com/legacy/wileychi/gis/volumes.html

Next week

• We will look at overlay – a key tool in GIS• How can we overlay objects which represent

fields and entities - what different implications do the conceptual data types have?do the conceptual data types have?

• How does overlay work – in particular the use of topologytopology

• What errors can arise when we perform overlay?overlay?