Geograhical aspects of the Barbados National Transport database

Geograhical aspects of the Barbados National Transport database


Keith R Johnson1 and Nigel R. Marshall2
1Transport GIS Consultant, Span Consultants

2Senior GIS Specialist, GeoCaribe

Barbados is the most easterly of the islands of the Caribbean. Its geographical location is 13 degrees north, 59 degrees west. It is a small island of 166 square miles or 432 square kilometres. (see Figure 1). It rises to a height of some 340 metres above sea level. It is composed of mainly limestone and this provides for its good drinking water, as the rain is filtered through the limestone into an underground aquifer and pumped back to the inhabitiants. The population is 265000 persons, of which about half live in Bridgetown the capital..

The Lands & Surveys Department was established in 1966 to provide mapping and land surveying services for the island. It is the repository for all legal (cadastral) survey plans. It provides and maintains the vertical and horizontal trigonometrical control for the surveying profeesion. It provides surveying services for the acquisitions of lands for housing and other social projects. The latest being a 20Ha land acquisition for the relocation of persons affected by the airport expansion. This project entailed compulsorily acquiring land for the expansion and also land for the resiting of the persons so affected.

Barbados National Transport Plan
The ToR for the Barbados National Transport Plan(1995) required that a National Transport Database (NTDB) be established. Form the outset it was decided that there should be a geographic dimension to the NTDB. Of course not all data that should be in a NTDB will be associated with individual geographic locations, for example, national statistics such as tax revenues, tourists/ visitors, cruise ship arrivals, aviation statistics. Having recognised that information about roads for example was at least as important as the geograhic representation of those roads MapInfo was chosen. (Microsoft Excel Worksheets can be read directly into MapInfo).

At the time there were two GIS – an ILWIS GIS set up by the Ministry of Agriculture and an ArcInfo GIS set up by the Coastal Protection Unit. Information was shared with both.

A key component of the tools to prepare a transport plan was a road assignment model (TRIPS). The road network was computerised as a set of straight lines between road junctions. Using this, albeit implified representation, allowed road characteristics such as width and traffic flows to be graphically represented and also bus routes to be displayed very early in the Study. Each road link was assigned an unique identifier of the form – XXXX.nnn where XXXX was the road name and nnn was a sequence number.

The information about the road sections was stored using these unique identifiers and the geographic representation of the road sections was stored also using the unique identifiers. In this way additions/ amendments/ corrections could be made to the information stored about the road links without any change to the geographical representation. In a similar manner the geographic represenation of the road links could be refined without any change to the information.

As was common practice the road network was drawn on 1:10,000 scale maps in the urban areas and 1:50,000 maps in the rural areas. One of God’s gifts to Barbados is its shape and size – the island fits almost perfectly on a single A1 Sheet. Twelve 1:10,000 sheets cover the whole island. The straightline representation of the road network in the urban area of Bridgetown, the capital was readily understood, however the straight-line represenation in the rural areas was not so readily understood. Thus the priority was to to refine the digitisation of the rural roads. This was done by scanning the 1:50,000 Map Sheet (1993) and the using MapInfo’s on screen digitising facility (sometimes referred to as heads-up digitising). Whilst the geograhical representation was being refined information from the Road Maintenance Management Study was abstracted and coded for each link The original data was stored as chainages along a road.

The bus routes were coded as a sequence of road links. Whilst this was being done the urban and rural networks were refined further using 1:10,000 map sheets (1986). In a similar manner to the 1:50,000 sheets the twelve 1:10,000 map sheets were scanned and useed for on-screen digitising.

The Enumeration Districts (Census) were first digitised from an assortment of scans of “Census Maps” and then checked by overlaying the 1:10,000 maps.

The datasets included in the GIS were :-

  • Demographic – 1990 Census, Traffic Zones
  • Education – Scholl rolls and school zones
  • Main Road Network and Junctions
  • Road accidents
  • Public Transport – Barbados Transport Buses, Mini-buses, ZRs (Route Taxis)
  • Rasters – 1:50,000 Topographical, 1:50,000 Geological

This year’s National Census (2000) has been successfully carried out and is now available to appropriate bodies in digital form. Post – National Transport Plan
Following the completion of the National Transport Plan the GIS was extended to include all the roads for which the Ministry of Public Works was responsible. The additional roads are mainly access roads. These were added to the Road Network. The node-link structure comprising the main road network was not amended – the access/ minor roads were a separate dataset that could be displayed with the main roads.

A Road Safety Study was undertaken in 1997/8. The NTDB GIS was used as a basis for recording all the traffic signs and road markings.

The facility to prepare maps almost instantly helped in the co-ordination of road maintenance, laying of new water pipelines, putting telephone lines underground etc to minmise traffic disruption.

Environmental Assessment Study
In 1997, Government embarked on a major environmental assessment study. It was called the Environmental Management and Land Use Planning Project (EMLUP). It encompassed all the datasets from all the agencies and has now been implemented in the Town and Country Development Planning Office. The Lands & surveys Department is going to have new datasets hopefully by August 2001 to update the existing digital topo maps. Ministry of Agriculture is conducting a study using GIS within the Scotland District to provide hazard mapping and soil susceptibility to erosion. The Coastal Zone Management Unit is running their GIS to aid the Town Planning in planning decisions along the coastline. It also is using GIS for coastal vulnerability studies.

Department of Lands & Surveys
The Department presently has a staff of 40 persons. 11 surveyors, 14 surveyors assistants(chainmen), 11 CAD drafters, Chief Surveyor and other administrative staff

The mapping available for sale comprises :-

  • 1:50000 covers the entire island on one sheet (1993)
  • 1:25000 covers the entire island on two sheets
  • 1:10000 covers the entire island on 12 sheets (1986)
  • 1:5000 covers the entire island on 97 sheets (1974) and more recently (1984) covering south east cosastline
  • 1:2500 covers the south of the island (vector)
  • 1:1250 covers the south west and west coasts

All the above are available in a digital format.

In common with many other countries much of the mapping is quite dated. However, the Cabinet approved, on November 23 2000 , a sum of money to capture new aerial photography and then have planimetric extraction done to provide an up to date digital topographical base map to be used in a National GIS, of which Lands & Surveys will be the coordinator.

The authors acknowledge the encouragement of the Government of Barbados and the assistance of their colleagues

Figure 1 Location Map

Figure 2 – Barbados Main Road Network