GIS@development December 2001; Urban Information System

The application of current technologies of aerial photography, photogrammetry, satellite imagery and now GIS and GPS, have been discussed since early eighties for the town and urban planner but, it appears, not by the planners. The efforts of the Central Government Departments and others, namely Indian Institute of Remote Sensing (IIRS) and National Remote Sensing Agency (NRSA) have been fruitful in generating base maps. However, the number of towns that have been mapped remains even below 200.

According to 1991 census there are more than 4,000 urban settlements in India. Out of these, 500-600 towns that technically come under the category of class A and B urgently need base maps for normal ‘planning activities’. Till today, out of 500 – 600 towns, only 170 towns have regular maps. If we include the large-scale town maps required by the engineers and property managers, the requirements for the urban mapping can take on gigantic proportions. The solution has, therefore to be found out by judiciously applying these modern technologies to planning problems.

Existing resources
Satellite Imagery from IRS-IC, IRS-ID is available with NRSA. Information about geology, soils, forestry, ground water, irrigation, etc. is available from the concerned Government Departments, but not on scale larger than 1:50,000. It follows that urban planners are not benefited by these efforts at national scale. Therefore if there is a GIS project pertaining to an urban area and large scales, the physical inputs (layers) have to be generated separately as a project itself (Table 1).

**Table 1:** *Making the best of existing resources*
Resource	Method	Cost
1:25000 map(s) Survey of India, covering the town	Enlargement of maps. The geometry of some of the points/features is acceptable for diluted specifications of the town-based-maps. The updating can be done on 1:10,000 enlargements in the field	Rs 30 to 40 of per hectare
Geo-coded satellite imagery of IRS-C, IRS-D. NRSA	This imagery provides 1:12,500 scale photographic or digital imagery of an area of 9km x 9 km centred around the point/area of interest	A resolution of 5.8 meters, is about Rs. 7000/-
Example Urban planners have used the imagery of two time epochs to detect changes (unauthorized) in Rohini area of DDA. (Ref. Uttarwar, P.S on http://www.gisdevelopment.net/application/urban/overview/urbano0015.htm) Budget Cost : Rs. 40 to Rs. 50 per ha.

Needs of an urban planner
The requirements of the urban planners, administrators, engineers, environmentalist and cadastral surveyors these days, are not satisfied on the scales of 1:10,000. The maps are required on larger scales of 1:4,000 (to match with cadastral records) and even larger i.e. 1:2,000 to cater to the engineers and utility (water supply, electricity, communication) establishments. The solution for such large-scale maps has to be found in the technology of aerial photography, photogrammetry and ground control by GPS.

The proper GIS for a town can only be made when all the data-base adheres to rigid specifications. Some unfortunate practices of using inappropriate technologies, namely plane tabling or satellite imagery for very large scales have crept in due to the misplaced enthusiasm of producing urban

GIS projects no matter what the accuracy -scale relationship of the base topographical layer of the GIS project is.

Approach to the technological solutions
The mapping resources of India are very limited. To augment these some private firms have now entered in the mapping field by employing sophisticated technologies. Some of the points to be kept in mind are:

The specifications of the map outputs should be evolved for maximum benefit to the user. Sometimes, the specifications can be diluted (in consultation with the map-makers) in case benefits are in terms of reduced ‘time’ and ‘cost’. This approach is likely to satisfy ‘more cities’ with less investment.
The initial design of the aerial photography, survey-field control methods etc has to cater to the requirements of the users. The contents and the information base have to be designed accordingly. Digital database is generated keeping in mind that hard copies are always required (Table 2).

Users requirements
The table 2 indicates the needs in terms of requirement of scale of maps and information on the elevation (height). It also makes clear that producing urban maps on different scale is not a big problem provided the contents of the digital data base can be properly stored through the application of GIS. The need, therefore, is to standardise a few scales e.g. 1:2,500, 1:4,000 and 1:10,000 so that users can be trained and sensitised to work on these standard scales, attributes and elevations/contours etc.

**Table 2:** *Scale and heights for variuos function*
Functions	Scale	Height/Contour Interval (C.I)
Planning Industrial Sites	1:4000 to 1:5000	2 meters
Engineering Plans	1:2000 to 1:5000	1 meter C.I + Bench Marks
Housing	1:2000 to 1:4000	1 Meter C.I + Bench Marks
Transportation	1:5000	1 Meter C.I. + Bench Marks
Traffic	1:1000l Maps of traffic intersection
Engineering	1:1000	Levelling along the alignment
Water Supply & Sewerage, Waste disposal	1:2000 to 1:10000
Roads etc.	1:4000	1Meter C.I. + Bench Marks
Regulatory
Revenue Authorities	1:2000 to 1:4000	Corelation with existing Land related subjects revenue map
Jhuggi Jhopri Clusters	1:2000 to 1:4000
Jhuggi Jhopri Clusters	1:2000 to 1:400
Land Resources	1:10000 to 1: 25000	5 metres
Ground Water	1:10000 to 1:15000	5 metres
Drainage, surface water	1:10000 to 1:15000	5 metres
Environment
Inventory of vegetation, trees, parks etc	1:4000 to 1:10000
Heritage sites, monuments	1:2000	1meter C.I

Urban Mapping Methodology
This section briefly describes the production processes of the various technologies to provide a general idea for facilitating effectiveness at the policy – making level.

Aerial photography: Aerial photography is generally carried out by the National Remote Sensing Agency (NRSA), Hyderabad. The Aerial Photography for digital-data-base for urban mapping is designed in such a manner that the significant ground object of the smallest size is clearly visible on the photograph.

A scale of 1:8000 is considered optimum for this purpose. The minimum size object of 20 cms can be discriminated against a suitable background of the ground. For example, all manholes in a city can be mapped easily from 1:8,000 scale aerial photography. Cost varies on the distance from Hyderabad. Rs 30 to Rs. 40 per hectare for Delhi and surrounding areas.

Security Environment for Aerial Photography: All fresh Aerial Photography is classified as ‘secret’. NRSA has, therefore to take clearance from the Ministry of Defence on behalf of the client. The clearance is also required for the productive use of the Aerial Photography. These activities generally take 3 to 4 months in case the firm order is placed with NRSA.

Undertaking of the actual flying (Aerial Photgraphy) and other clearances from DGCA do not take much time. The flying season is reckoned from September to March. It, therefore, implies that project formulation, sanctions etc should finish well before flying time. The modern camera, which NRSA uses, is fitted with Global Positioning System (GPS) and Image Motion Compensation (IMC) device. This entails significant reduction of field control and improves the quality of aerial photography.

Ground Control for Photogrammetric Process: When Photogrammetry is employed as the main production technology, there is considerable (almost 60 to 70%) reduction of control work in the field. However, photogrammetry stipulates a minimum number of ground control points at proper location with respect to the incidence of aerial photograph (model) on the ground. These ground control points are marked very accurately on the aerial photograph and form the first and the most important input to the process of photogrammetry.

Pre-Pointing/Signalisation of Ground Control Points: Ground control points are used to orient the aerial photographic model (stereoscopic model) for scale, elevation and accuracy. Some ground points which are small in size, peculiar and symmetrical, so that these are identifiable on aerial photographs, are chosen. As an example, X, Y, Z co-ordinates to a few of traffic – roundabouts while doing fieldwork for establishing ground control points for photogrammetry are picked up during field surveys.

Monumentation of Ground Control Points: It is prudent to provide some permanent pillars (X, Y, and Z co-ordinates) at suitable places, which not only will help in the photogrammetric processing but also will provide permanent references on the ground.

Connection of Ground Control Points to Survey of India Stations/Bench Marks: It will suffice for the objectives of urban mapping if an arbitrary origin for X, Y, co-ordinate system for URBAN DIGITAL DATABASE is established. The reason obviously lies in the security environment of the country. There could be some hassles if Survey of India Trigonometric Station is connected to the information system.

The above concept is, however, not extended to the elevation system. Survey of India benchmarks within urban area and, outside will form part of the ‘levelling system’. Further additional levelling benchmarks along the main roads/streets of the town should be established.

Aerial Triangulation and Photogra- mmetric Plotting/Mapping: This is a photogrammetric operation in which initial field control (as mentioned earlier) is augmented by a set of procedures on a photogrametric machine. The result is that the aerial photographs (stereo models) will have control points at optimum places. These control points obtained after aerial triangulation are marked on photographs and are required for producing mapping details (X, Y & Z). This process is known as photogrammetric plotting/mapping.

The digitisation of all the physical details of the map and the ‘elevation’ is done mechanically while ‘plotting’. Thus in present day Photogrammetric machines the map output can be obtained as hard copy as well as in digital form. It is quite possible to generate Digital Terrain Model (DTM) for subsequent incorporation in the Geographic Information System.

Photogrammetric Output: The output can be in digital as well as hard copy.

Planimetric The requirements or planimetric accuracy are easily met in photogrammetric plotting and are seldom critical. An accuracy of 20 cm to 30 cm in plan can be expected.
Contours: Generally accepted tolerance is that only 10% of all checkpoints may have an error larger than half the contour interval. Maximum error in height that should be expected is 1/5th of contour interval. An accuracy of + 20 cms to 40 cms can be obtained from 1:8,000 scale Aerial Photography (flying height 4,000 feet)

Cost of Photogrammetric Plotting

Scale

1:2,000
1:5,000
1:10,000

Cost/per hectare

Rs 500 to Rs 700
Rs 300 to Rs 600
Rs. 150 to Rs 250

Field Verification of Photogrammetric output: There are many physical features, which are not photographed or are omitted e.g. houses under trees, underground pipelines etc. which can be checked by ground visits. (Cost Rs 25 to Rs 40 per hectare)

Digital Urban Orthophoto: Orthophoto is an Aerial Photograph which is scaled to the desired scale, say, 1:4,000 and from which all distortions due to the ‘tilt’ and ‘relief’ are removed through digital photogrammetry. In other words Digital Urban Orthophoto is a photo-map on which all measurements can be done and it is geometrically equivalent to a map.

Digital Urban Orthophoto is a useful product, which can be produced with a minimum of groundwork. Urban planners should in fact get used to this product as a reliable base-map (Cost Rs 300 – Rs 400/hectare)

Urban GIS: GIS is basically, a comprehensive spatial ‘decision support system’ based on (a) geo-reference digital data base (b) computer hardware/software (c) non-spatial attribute data. The distinguishing and most advantageous feature of GIS is the use of the location of features in spatial system/co-ordinate space as the fundamental referencing system. The spatial data is obtained from satellite imagery, aerial photography/photogrammetry, field surveying and ground visits.

Today GIS, can be applied in towns for creating urban cadastral land suitability analysis, landscaping, land use modelling (forecast), environmental impact assessment of human settlements, urban growth, location allocation of utilities/facilities, traffic planning, air pollution studies and hazard studies etc. The land resources information which is required essentially for any modelling e.g. ground water, soil characteristics waste land can be gathered from satellite imagery.

Revision and updating of Urban Digital Database: Preparation of Geographic Information System for any city will entail efforts in generation of physical database. This is a common scenario in India, as all the information required for GIS is not readily available. Therefore almost 60 to 70% of preparation of GIS goes in generating the database.

After the database is prepared through photogrammetric process, it is important to update the database and record major physical changes that take place on the periphery of the town regularly.

It is therefore suggested that the digital database should be kept updated every 5-6 months with the help of aerial photography and satellite imagery supported and verified by ground visits.

Satellite Imagery and Remote Sensing: Indian Satellite IRS-IC and IRS-ID have the resolution of 5.8 metres. NRSA has been commercially delivering 1:12500 scale photographic output of these satellites whose cost of Pan Sensor (black and white) based product is Rs 7,000 for an area of 9 kms x 9 kms. Photographic product on 1:12,500 scale may not provide the most desired base-map but is sufficient for general information. Since the satellite visits the same spot every 24 days, it is possible to do monitoring of urban phenomenon subject to the resolution of 5.8 metres. Many urban authorities like DDA have used satellite imagery for monitoring landuse changes.

The good news for a town planner is that satellite imagery from IKONOS (USA Commercial Satellite) and India’s Technology experiment Satelite (TES) are capable of providing 1 metre resolution satellite imagery. IKONOS is already operational. The base – maps of towns can, therefore be conveniently prepared and updated with the help of high-resolution imagery. The technology based on high resolution imagery will be time and cost effective.

National Thrust on Information Systems on Internet: Department of Space, Department of Science & Technology are trying to create a National Spatial Data Infrastructure (NSDI). This initiative will create a forum/platform for almost all data generating agencies to meet at one place and carve out well-integrated programmes for India. The user Ministry of Urban Development along with their counterpart in the state should put up their considered demand for Urban Information System.

Almost all towns of India should have a regular base map following the principle of having public private participation including the large geographic and planning community. The ultimate aim, say, for the next five years should be to have the desired basic information on the internet/intranet so that public at large can participate and benefit from the spatial information. The technology of Airborne laser Terrain Mapper and large-scale Radar Sensing are around the corner. Let the urban planning community gear itself to harness it. It is justifiably claimed that what you have not been able to survey for some months, can be finished in days by harnessing latest technologies.