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3.4 Application layers

Google Maps API, which includes the Google Satellite, Physical and Hybrid layers, are the most readily available source of good resolution satellite imagery and geographic data, but are subject to withdrawal or alteration and can sometimes be of variable quality (Crampton 2008, 93). The API also limits both the quantity of data requested per day and the resolution of any static maps produced from the data (Google 2012). Nevertheless, due to the familiarity that users have with Google-style mapping in general and the high quality of the satellite imagery, Google layers were included in the application.

Owing to current and potential future restrictions imposed by Google, a FOSS map source called OpenStreetMap (OSM), which provides free global geographic data, was included in the application. The OSM project uses the same peer production model as Wikipedia to create free map data (Haklay and Weber 2008, 13). OSM collects its own data and as such has no copyright restrictions or issues relating to third party such as NAVTEQ or Tele Atlas (Crampton 2008, 94). OpenStreetMap lacks the detail of comparable modern Ordnance Survey products, but this loss of detail is arguably mitigated by the low cost of use and offset by the inclusion of historic map and aerial photographic layers within the WebGIS that can provide relevant details, such as field boundaries, to the user. The utilisation of online content and services essentially means the application can be categorised as a mashup. This simplifies data storage issues and places less stress on the available bandwidth to the test environment. Coding, however, is not simplified to any great degree and manual mashup development is still often the prerogative of the skilled developers (Yu et al. 2008, 45). The incorporation of GeoServer into the software architecture also means that the application could be altered rapidly to serve bespoke mapping and satellite imagery, where available, ensuring the overall methodology is not reliant on third party data sources.

Historical map data was provided in the form of an overlay layer, which displayed a 1st edition Ordnance Survey map at 1:2500 scale, dating from 1873-85. This enabled users to establish with more certainty the relative antiquity of features through simple map regression.

Table 3: Layer data sources used by the application
Application Layers Layer Name
Google API(Satellite, Physical and Hybrid) Google Satellite
Google Physical
Google Hybrid
OpenStreetMap OpenStreetMap
Slope analysis of Digital Terrain Model LIDAR: DTM_Slope
Hillshade of Digital Terrain Model LIDAR: DTM_Hillshade
Principal Component Analysis of Digital Terrain Model LIDAR: DTM_PCA
Sky View Factor of Digital Terrain Model LIDAR: DTM_SVF
Ordnance Survey 5km grid overlay 5km grid
WFS-T User-generated features Features
1st edition Ordnance Survey 1:2500 1854-1949 © Crown Copyright and Landmark Information Group Limited (2012). All rights reserved. (1854-1949). 1st edition OS

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