Visibility analysis in the Stonehenge and Avebury World Heritage Site

Visibility analysis in the Stonehenge and Avebury World Heritage Site Paul Cripps GIS Specialist, Archaeological Projects, English Heritage [email_address] CAA UK, University of Southampton, January 21 st 2005.

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Introduction
The Stonehenge & Avebury World Heritage Site
The WHS GIS
Overview of visibility analysis
History of visibility analysis using the WHS GIS
Revised analysis - methodology
Revised analysis - results
Further work
Conclusions

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 The Stonehenge & Avebury World Heritage Site
Unesco World Heritage Convention
Inscribed in 1986 as two parts (C373)
Avebury: 22 sq. km.
Stonehenge: 26 sq. km.
Each part has a WHS Coordinator and a Management Plan

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 The WHS GIS - background
Set up in mid-nineties to facilitate assessment of Highways Agency A303 proposals at Stonehenge
Originally covered Stonehenge only
Now covers both parts with a wealth of data

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 The WHS GIS – system
Originally Unix-based ArcInfo system
Until recently used ArcView3.2
Migration to ArcGIS9.0
Maintained at EH Archaeological Projects, Portsmouth
Users based in EH (Bristol & Amesbury) and Kennet District Council

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 The WHS GIS - data
Variety of datasets
Primarily for management purposes
e.g. designations
e.g. published road scheme
e.g. basemaps
e.g. terrain models
e.g. archaeology and geophysics
But also a research tool, supporting Stonehenge Research Framework (Bournemouth University)
e.g. revised dating for Stonehenge sites

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Overview of visibility analysis - basics
Inputs : Raster/TIN elevation model & observer/target locations and offsets
Output : Raster coded 1 (visible) or 0 (not visible) ie a simple binary viewshed
Processor intensive: many calculations with unoptimised viewshed algorithm
Vectors: have both magnitude and direction, so a positive line-of-sight A ->B does not necessary imply B -> A (unless we assume reciprocity of vectors)

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Overview of visibility analysis – cumulative and fuzzy techniques
Cumulative viewsheds comprise a number of summed viewsheds from >1 input locations
Cell value indicates number of input locations visible from cell or number of input locations which can see cell (assuming reciprocity)
Fuzzy viewsheds incorporate controlled error into analysis
Monte-carlo approach to produce a distribution of viewsheds
Cell value indicates probability of seeing input location from cell or probability of cell being visible from input location (assuming reciprocity)

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Overview of visibility analysis – fuzzy viewshed
Calculated from Stonehenge
OS LandForm DEM, 10m resolution
1000 iterations
Uniform error surface
±2m approximates error in OS LandForm
Gives a better approximation of visual envelope associated with the henge: Shades of grey vs. black & white

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 History of visibility analysis using the WHS GIS
First analysis undertaken 1997 (Batchelor, 1997)
Used a 50m quadrat approach
13 sites for Stonehenge
6 sites for Avebury
Used to produce visual sensitivity maps for use in management plans
Occasional ad-hoc analyses since relating to planning applications
143350 415050 Woodhenge 141750 410200 Winterbourne Stoke Group 141620 414600 Vespasian's Camp 142220 412220 Stonehenge 144200 409300 Rollestone Camp Tumuli 145900 410200 Robin Hood's Ball 142950 413700 Old Kings Barrow Group 142250 413433 New Kings Barrow Group 140200 410830 Lake Barrow Group 145198 412800 Durrington Barrow Group 142800 411850 Cursus Barrow Ridge 141390 413450 ConeyBury Hill 141300 411655 Bush Barrow Northing Easting Location 167737 410454 West Kennet Long Barrow 168530 410010 Silbury Hill 169310 410340 Waden Hill 168025 411827 The Sanctuary 169980 410240 Avebury Henge 171460 408720 Windmill Hill Northing Easting Location

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Revised analysis - methodology
Same elevation model; OS LandForm, 10m resolution but no quadrats
Same sites; 13 for Stonehenge, 6 for Avebury
500 iterations per site to produce individual fuzzy viewsheds
Scripting accomplished using Avenue for ArcView3.2
4500 viewsheds calculated in total, taking 1-2mins per viewshed, about 75 hours total processing time to produce data
Fuzzy viewsheds summed to produce cumulative fuzzy viewsheds
Cumulative fuzzy viewsheds used to produce visual sensitivity maps

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Revised analysis - results
Fuzzy viewsheds provide better approximation of visual envelopes for study sites
Cumulative fuzzy viewsheds provide better approximation of visual sensitivity wrt the input sites

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Revised analysis - Stonehenge results

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Revised analysis - Avebury results

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Further work
Can be used in conjunction with other datasets in the WHS GIS e.g. extensive geophysics from A303 evaluations
Detailed investigation of viewsheds for each site
Aim to improve error model to account for spatial autocorrelation of error: Topographic survey or LiDAR as independent dataset (after Carlisle) to build error surface

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Conclusions
Fuzzy approaches to visibility analysis provide better approximation of real-world situation
The visual sensitivity maps are a key resource within the site management plans
Are being used in discussions relating to WHS borders and buffer zones
Still room for improvement in the model

Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 fin

Visibility analysis in the Stonehenge and Avebury World Heritage Site

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