M. J. JACKSON* Planning lntelligence Directorate (3) Department of the Environment London, England P. CARTER lmage Analysis Group, MPD Hanoell, Oxfordshire OX11 ORA, England T. I?. SMITH Planning Intelligence Directorate (3) Department of the Environment London, England W. G. GARDNER lmage Analysis Group, MPD Hanoell, Oxfordshire OX11 ORA, England Urban Land Mapping from Remotely Sensed Data Results suggest that the Landsat resolution is compatible with the requirement to map developed areas of 5 hectares or larger. INTRODUCTION use to which land is put in the United King- dom (UK) has not been available. Claims HE DEPARTMENT of the Environment have been made by some environmentalists T(DOE) is concerned with collecting in- that land is being destroyed by urban devel- formation on both the extent and distribution opment at an alarming rate. While the lim- ABSTRACT:All developed areas, offive hectares or above, in England and Wales were mapped using aerial photography flown in 1969. The Department of the Environment is now undertaking research and development with the Image Analysis Group, Harwell to enable the monitoring of urban growth from this base year by Landsat imagery. It is necessary, therefore, that the automated classification of urban growth from Landsat data be comparable to the aerial survey. To ensure this comparability it is necessary to quantify the differences in the classification systems and to emphasize the use of ground verification procedures. Present indications are that the Landsat resolution is compatible with the DOE'S basic requirement to map developed areas of ouer five hectares, though the capability to monitor change with the high level of accuracy required has not yet been established. The paper describes the ground-truth checking procedures and problems en- countered in monitoring urban growth. of developed land in England and Wales and ited statistics available do not confirm this the rate at which land is taken up by devel- view, the need for more comprehensive in- opment. In general, information about the formation does exist if land-use policies are to be monitored quantitatively. To meet this * Now with ETSU, Harwell, Oxfordshire 0x11 requirement a survey of developed areas ORA, England. from 1969 aerial photography was completed PHOTOGRAMMETRICENGINEERING AND REMOTE SENSING, Vol. 46, No. 8, August 1980, pp. 1041-1050. PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1980 in 1978 and five categories of urban land use able for use with other data bases. This have been mapped at 1:50,000 scale. The stage constitutes a major undertaking and, maps cover the whole of England and Wales, because of the numerous manual opera- tions, is a common source of errors. and all "developed areas greater than five hectares have been digitized for computer The cost of the above three stages is high, processing and constitute the first national especially the acquisition of the data which data base of built-up areas. Further details may itself prove prohibitive. Also, while relating to this survey are given below and a there is a high level of redundancy in full description is given by Smith et al. 1:60,000 scale photography for national (1977). mapping restricted to urban land uses, this There is now a need to up-date regularly scale of imagery does not meet the needs of the initial data base. In order to test the county and local planning authorities where feasibility of using the Landsat satellite data, scales of 1:12,000 and greater are typical. the DOE and the Image Analysis Group of These factors and the increasing availability the Atomic Energy Research Establishment, of alternative forms of data collection mean Harwell, have developed a system for han- that it is important to consider other sources dling, displaying and classifying Landsat of land-use data which may be more appro- data (Carter and Jackson, 1976). The feasi- priate or cost efficient for the collection and bility of using the Landsat data can only be analysis of such broad national data. In par- checked by carrying out detailed "ground- ticular, the last few years have seen the in- truth" checks on selected test areas. troduction of side-looking radar imagery This paper describes the detailed check- (Henderson, 1977) for commercial and civil ing carried out to test the results obtained for purposes and spaceborne imaging systems the Landsat data and the consistency of clas- such as the multispectral scanners on-board sification of specific land-use parcels. De- the Landsat satellites. tailed results for one test area are presented. The use of Landsat imagery for informa- "Ground-truth," throughout the paper, tion at the national level overcomes many of will refer to land-use information collected the above problems related to the collection from aerial photographs, topographic maps, of data. Also, and most importantly, the cost and site visits and classified according to the of complete cover is very much less than for urban land-use class definitions used for the aerial photography. While the cloud prob- 1969 Developed Areas Survey. lem is not solved directly by the Landsat sat- ellites, the regular repetition of the orbits means that cloud-free coverage is likely at least on one or two occasions per year in the The data source for the survey of Devel- UK. The advantages of Landsat are now be- oped Land in 1969 was 1:60,000 scale pan- coming well known (see Anderson, 1977; chromatic aerial photography flown by the Gardner et al., 1977) and include the synop- Royal Air Force in 1969. There would be tic coverage and computer compatibility. three serious problems to be overcome, The potential of airborne and spaceborne however, if the DOE wished to commission radar fir urban mapping is less clear. The national aerial surveys on a regular commer- daylnight and cloud penetration capability of cial basis for the monitoring of land-use radar is an obvious advantage of this data change. source for areas experiencing the weather of These three problems are the UK. Complete cover of the UK by air- borne radar would be both quicker and The collection of data. Problems of air traffic control and particularly the cloudy cheaper than a photographic survey due to weather of the UK make comprehensive the far less stringent demands for "good fly- photographic cover on a regular basis both ing weather" and the wider swath-width of difficult and expensive. the obtained imagery. On the other hand, The handling and classification of data. neither manual nor automated interpretation Handling and organization of prints from has yet been demonstrated as being able to many sorties in itself creates problems. give sufficient land-use information to justify Classification of the photographs must be the cost of this data acquisition. undertaken by several interpreters, may Having assessed the feasibility of using take many months, and subjectivity in the classification procedure cannot be com- space imagery for urban monitoring at the pletely avoided. national level, the Department of the Envi- The computer processing of data. Fol- ronment is proceeding with research to es- lowing classification, the data must be tablish a rapid survey system based on digitized and processed into a format suit- automated techniques of interpreting and URBAN LAND MAPPING FROM REMOTELY SENSED DATA classifying images. It is expected that the The five categories are defined in detail following advantages will accrue for the suc- (DOE, 1978) with respect to the data sources cessful implementation of such a system: so as to obtain a high level of objectivity in the interpretation, which was undertaken by An increase in the amount and accuracy of land-use information for national and re- a commercial air-survey company. gional planning from regular and com- Using the above described "Developed prehensive surveys. Areas" maps, the outer boundary of the de- An increased ability to monitor trends in veloped area for a number of test sites has land use and to assess the spatial conse- been up-dated to the year of each Landsat quences of implementing planning classification with the aid of aerial photogra- policies. phy, maps, and site visits. The location of A reduction in time and manpower re- these sites is shown in Figure 1. The up- quired to produce national data. dating has not been applied individually to More objective information based on con- sistent criteria and related to a single time all the categories of use since the present base. research is concerned only with monitoring The application of the developed software change to the total developed area and not to a wider range of inventory problems with change of land use within those areas. than just urban land use. Urban open space (Category E) has, how- ever, been separately treated because the spectral return of such areas is similar to rural areas, and it has been therefore neces- The DOE survey of urban land use for sary to consider it as 'non-developed' for the 1969, referred to above, was used as the purposes of automated classification. While main source of ground-truth in assessing the it would be possible to add all 'non- accuracy of the Landsat classifications developed' areas wholly surrounded by new undertaken at Harwell. This survey mapped growth to the total developed area, new five urban land uses at the 1:50,000 scale in- peripheral urban open space cannot be so corporating all land-use parcels of five hec- easily incorporated into the total urban area. tares or more. The five land-use classes were Finally, all water surfaces of over five A. Residential. hectares have been separately mapped irre- B. Industrial and/or commercial. spective of their land-use category, which C. Education and/or community.