Computers & Geosctences Vol. 11, No. 3, pp. 309-310, 1985 0098-3004/85 $3.00 + .00 Panted m the U.S.A. Pergamon Press Ltd.

COULD LINPOINT BE ADAPTED TO A MICROCOMPUTER?

ALASTAIR MORRISON Department of Geography, University of Glasgow, Glasgow G I2 8QQ, Scotland

(Received 12 June 1984)

INTRODUCI'ION

Anyone whose experience of maps has been limited to computer-mapping packages could be forgiven for believing that only one type of map exists, the choropleth map, and that all mapped data refer to areas such as counties, districts, and so on. But, if we look at the range of hand-drawn maps in existence, it is evident that data relating to areas can be mapped in many forms other than that of the choropleth map, and that many data relate to points or lines rather than areas.

LINPOINT began when the only mapping package available at Glasgow was SYMAP. The GHOST graphics subroutines were used because they were the only ones then available in Glasgow University. I would like to acknowledge the help given by the consultants of Glasgow University Computing Service. This paper relates to Version 2 of the program described in Morrison (1981).

CAPABILITIES OF THE PROGRAM

LINPOINT will draw maps of quantitative or qualitative line or point data (Fig. 1), using a graph plotter or equivalent device. The program is especially convenient for use with British National Grid coor- dinates, but maps of other areas or in other units can be made. The scale of the desired map can be specified directly or indirectly by stating the desired height or width in millimeters, or both dimensions of the space into which the map is to be fitted. The user may specify a title, frame, numbered or unnum- bered grid, and legend, all of which will be adjusted automatically in position and size so that they fit within the available space without overlapping.

When the program is used to draw lines, each "link" is represented by a straight double or single line between the "nodes" at its two ends. The lines might represent, for example, roads, rivers, air or sea links, migrations, or imports or exports. The user can control the distance apart of the two lines and their color and thickness, and the lines may be broken in a variety of ways. Map-type I is a simple location map having double or single lines. For Map- type 2 the quantity being represented, for example road width, is divided by numerical boundary values into a number of classes, such as narrow, medium, and wide, and the classes are represented by line symbols which differ in one or more of the charac- teristics mentioned. In Map-type 3 (lower left in Fig. l) the distance apart of the two component lines is

made directly proportional to the quantity being represented, such as road width. Map-type 4 (lower right in Fig. l) is a combination of types 2 and 3, in which the distance apart of the lines is proportional to one quantity r, which, for example, might be road width, but the other characteristics of the line symbols, namely continuity, thickness, and color, are deter- mined by the class into which the line falls according to another quantity c, which might represent, for example, official road classification. On any of these map-types link names or numbers may be written along each link, class numbers may be inserted in the middle of each link, and place names or node numbers may be attached to the ends of each link.

The program also will plot point distribution maps, such as finds of stone axes (archeology), direction of dip of a rock layer at various points (geology), or features which can be treated as if they were located at points on a small-scale map, such as campsites, airports, villages, or towns. A range of mapping types exists similar to that available for lines (top right of Fig. l). The user can control the shape, size, color, weight, and orientation of the point symbols used. All points in one data set are labeled in the same size and style, determined by the user. The labels may be placed in one of eight positions in relation to the point symbol, for example, above and to the right. If desired, the position of each label may be specified individually and subsequently altered so as to avoid overlaps. The symbols may be left unlabeled, or they may be labeled with a number or a name.

Data relating to census districts or counties may be plotted by graduated shadings inside squares or circles centered within the district, proportional in size to, for example, the population. This avoids the undue visual prominence given to rural areas in nearly all choropleth maps of census data and also removes at one stroke all the costs and problems associated with digitizing district boundaries. Indeed, maps of data from the British 1981 census can be produced by LINPOINT directly from the standard output of the SASPAC 2.5 package, using the coor- dinates of the centers of the enumeration districts which it includes. No reformatting is needed. The typical cost of such a map, £5, is an order of magnitude less than that of maps produced by the package generally used. The point-labeling facilities provide a convenient way of identifying the shaded symbols representing districts or counties, as in the central and upper left panels of Figure 1. If the exact

309

310 A. MORRISON

N N I 24 25

f

m m m m l m m l m m l m m m m m |mmmmm|mmmummmm| mmmmm mmmmmmmmm mmmmmmmm wmmmmmm mmmmmmmmmmmmmmmm mmmmmmmmmummmmmm mmmmmmmmmmmmmlmm

TAYSI~

~ I E $ & GALL.~J

~ d

.>281~39 C 0 j ,

d 2

Figure !. Selection of types of maps

,e // \ which can be produced by LINPOINT.

location of district boundaries is important to the understanding of the distributions revealed, then the LINPOINT map can be plotted at exactly the scale of an existing map of Enumeration District boundaries and overlaid on it using a light table.

Several functions are performed automatically by LINPOINT, including the spacing of the grid, size and placing of the title, which is always at the head of the map, and placing and arrangement of the legend and scale, always to the right of the map. These features can be included or excluded, but the detailed arrangement is not under the user's control. This was a deliberate choice in order to reduce the number of parameters to be described in the manual and to keep it simple.

COULD LINPOINT BE ADAPTED TO A MICROCOMPUTER?

LINPOINT was written for mainframe use. In the interests of portability is was written in standard FORTRAN IV and a computer word length of 4 bytes was used. It has a straightforward relationship to the operating system: there are no workfiles to set up, and none of the input files need to be rewound. Input is directly from character files, and there are no binary "saved" files to confuse the inexperienced user. One weakness at present is the user interface. A microcomputer would permit more sophisticated, concise, and friendly control of the program than is possible from a dumb terminal.

Could LINPOINT be run on a micro? I would be happy to be persuaded that it could, but I see several reasons why it could not. If we think in terms of a

first-generation micro with 64K of memory, then it might seem at first sight that LINPOINT would fit into it, because the compiled program occupies under 32K bytes for program code and under 32K bytes for data. However, in most micros a large proportion of the 64K of addressable memory is taken up by an interpreter for the BASIC language, and in any micro with decent graphics much of the remainder will be taken up by the screen display. Therefore, the program could not fit on a micro without some type of overlay arrangement using floppy disks.

A second set of requirements which might not be met is a FORTRAN compiler for the particular micro, and an operating system able to handle disk data files for use by FORTRAN. The biggest problem, however, is that LINPOINT relies on calling graphic subroutines from the GHOST library. This would add substantially to the storage required, even if a version suitable for micros were available; this would have to include a postprocessor for the particular micro.

On the latest generation of microcomputers, with their ability to cope with an enormously greater amount of memory, these limitations might be over- come if it were considered worthwhile. Perhaps the optimum arrangement, however, might be to use a small microcomputer merely as an intelligent terminal providing friendly control of the program, which continued to be run by a mainframe.

REFERENCE Morrison, A., 1981, LINPOINT: a program for drawing

maps of lines and points: user manual: Geogr. Dept., Glasgow Univ., Occasional Paper Series no. 6, 75 p.