Best practice guidelines for the design, production and presentation of vacuum formed tactile maps

Simplification, symbolisation, and spacing

This next stage involves editing source material to include only the information to be reproduced in tactile form. Tactile maps are usually much simpler than visual maps as tactile discrimination between symbols is much coarser than visual discrimination. Figure 14 shows a base map drawn from the source material presented in Figure 13.

Avoid including excessive information (clutter). Using a range of heights for symbols can also reduce clutter in vacuum formed maps.

In standard cartographic practice map symbols are classified into three different types [38], and tactile map symbols may be similarly grouped:

When a satisfactory version of the base map is ready, the design should be transferred on to the base layer of the map mould. Rigid card, 1.5mm thick, is a suitable base material as it does not distort when symbols are attached with most types of heat resistant adhesive. In addition, it can be drilled to aid venting and is thick enough to enable water symbols to be recessed by cutting out an appropriate shape. The cut-out sections may then be underlaid with corrugated card to represent water features.

Early work on symbol design by Nolan and Morris [39] and James and Armstrong [40] was centred on vacuum formed reproduction and led to the development of the tactile map symbol sets marketed in the UK by RNIB (see Figure 15).

These symbols were intended as a standard symbol set for tactile urban maps. It is possible that a series of symbol sets might be recognised for different applications, for example a set for golf maps and another set for maps of countryside areas (see Tables 1, 2, 3, 4, 5 & 6, in pdf format). However, it is inevitable that any tactile symbol will have more than one meaning across a range of types of map, as there are not enough individually discriminable symbols to allow each to have a unique meaning.

Samples of materials to be used for symbols should be placed on the base map to get some idea of their suitability. These materials should capable of resisting a temperature of around 160 deg. C without shrinkage, distortion or melting. In addition, symbols should not be undercut as this prevents separation of the PVC foil from the mould; a slight outward sloping angle on vertical surfaces eases separation of map from mould (see Figure 16).

Information about symbol dimensions before and after processing, as set out in Tables 1-6, is included as a guide to choosing symbol materials. The choice will be made easier if the following suggestions are considered:

Some adjustment of the map design might be needed to accommodate sufficient separation between symbols. In addition, it should be remembered that the thickness of the PVC foil will have a significant effect on symbol sizes in the final product relative to the mould. Lines and point symbols should be separated by 5.0mm in the mould, although where there are clear height differences this may not be essential. Point and line symbols may be superimposed on area symbols, as long as there are sufficient height and textural differences. Trials of draft versions of maps with visually impaired people will solve any complexities of spacing and discriminability.

It is possible to design successful maps without using braille labels as long as each symbol used is discriminable from all the others included on the map. (Apart from the title, scale, and key, the author has only used braille labels on street maps. This has not presented a problem with interpretation for any users). A separate braille label sheet can be designed to use as an overlay.

When a designer can identify each component on a finished map mould by touch, it should be given to one or more visually impaired people to test. If the visually impaired tester(s) can discriminate all parts of the design without any problems, the mould can be prepared for vacuum forming. Vent holes 1.0 - 1.3mm diameter must be drilled through the mould at regular intervals, to assist the extraction of air from the space between it and the PVC foil. These holes should be drilled at approximately 25.0mm intervals along edges of line and area symbols, and more frequently around point symbols, to allow full evacuation of air from between the mould and the PVC sheet (see Figure 17). The greater the detail, the more vents are needed to ensure the best possible replication.