SECTION 7
Special purpose, scientific or thematic mapping must be plotted onto accurate geographic information of the study region which acts as a reference. This geographic information is a base map and is normally obtained directly or indirectly from available reference mapping, with hydrographic charts and topographic maps being the most common sources. In some studies the thematic information is added directly to available reference mapping. This is an economical and rapid approach, but one which can lead to excessively complex or cluttered presentations.
A better but more costly and slower approach is to create a base map designed specifically to display the thematic information by redrawing those geographic features which are significant to the subject and eliminating or simplifying the remaining features. Occasionally aerial photographs or satellite images are substituted as a simple base or photogrammetric techniques are used to derive a base map from these sources.
In general, base map information should be obtained at larger scales than that planned for the product to avoid the random filtering effect of generalization. The level of information, symbolization and accuracy of small scale maps are unsuitable for significant enlargements.
Some fundamental considerations for base maps include the following:
The level of base map detail is dependent on the purpose for which the derived map is required. Available reference maps are often too complex to be used directly as base maps.
The known or probable level of accuracy of the reference map must be given consideration and must suit the accuracy requirements of the new product. Standards should be checked and publication dates noted. Reliability diagrams or notes should be carefully inspected.
Projections can have a considerable impact on the suitability of base map material and on the economics of a whole project. Obtaining usable base material on a suitable projection is sometimes difficult but well worth the effort. A common problem is that thematic information must be plotted on available reference mapping which is based on a totally different projection. This necessitates knowledge of the characteristics of both projections and the time and capability to transform one into the other. The information required to perform this task may not be readily available, such as the location of the chosen parallels. In general these concerns are relevant to small-scale mapping. On medium and large-scale maps the consideration of projections is not normally a major problem.
The cartographer should remember that there can be a great range of scales within a small-scale map due to the map projections. The Mercator projection is a good example: a given symbol is four times larger in map area at 60° latitude than it would be at the equator. For that reason, attention must be given to the level of symbolization and compilation carried out in tropical zones in comparison to higher latitudes.
The following is a list of readily available small-scale base maps:
i) the General Bathymetric Chart of the Oceans (GEBCO) at a scale of 1:1,000,000 (Figure 7.1);
ii) the International Map of the World (IWM) at a scale of 1:1,000,000;
iii) aeronautical charts (ONC, WAC) at a scale of 1:1,000,000;
iv) the International World Map at a scale of 1:2,500,000;
v) maps in reference atlases generally at scales varying between 1:25,000,000 and 1:10,000,000 or smaller. Examples of these atlases include the following:
| a) | Times Atlas of the World (London); |
| b) | Atlas Mira (Moscow); |
| c) | series maps of the world at a scale of 1:5,000,000 published by the American Geographical Society (AGS), and by the Institut Géographique National (IGN) in France; |
| d) | series of maps of the world at a scale of 1:10,000,000 published by the IGN. |
Sources of base map information on any complex map product should always be identified, particularly when several sources of varying accuracy have been used. If permission has been obtained to use copyrighted materials the credit must be given exactly as specified by the copyright holder. The following are possible sources of base maps or base information:
i) In many countries the major mapping agencies can supply printed or film copies of hydrographic and topographic products in single colour format (black and white). Film positives are particularly useful as diazo copies (refer to Section 12) can then easily be produced for use as base maps for plotting data, trial interpretations and design studies. As mentioned earlier, overprinting thematic information directly onto these products is economical but results in the visual conflict of two different data sets;
Figure 7.1 Assembly diagram for GEBCO sheets. (Intergovernmental Oceanographic Commission and International Hydrographic Organisation)
ii) Orthophoto or photo maps (refer to Section 8) can sometimes be used as base maps. These can be economical to produce, and they have an implicit accuracy which many people do not attribute to line mapping because of the possibility of bias, error or manipulation in the production of the latter. The photo imagery must be reproduced in a light tone in order to allow the thematic information to be clearly visible. Photo base mapping has become popular for public presentations and tourist mapping;
iii) Satellite imagery, Landsat for example, can often be used for small-scale base mapping if its geometric distortion is not a problem. It can be treated in the same way as photo mapping. These images have a “high tech” connotation which can be a useful asset in many kinds of presentations. The images are widely available and current. Inquiries for information regarding satellite imagery may be addressed to: Earth Observation Satellite Company, 4300 Forbes Boulevard, Lanham, Maryland 20706, U.S.A.;
iv) Portions of published hydrographic charts or even topographic maps can be used directly. A negative of the map sheet is obtained from the mapping agency concerned, and unwanted detail is simply opaqued or masked. Photographic scale adjustment can also be carried out. The negative can be used to produce a new base map onto photographic film on which minor adjustments and line touch-ups can be made with an ink pen;
v) Single aerial photographs can often be used as base maps, particularly for small area/larger scale studies. The photograph, or a portion thereof, can be enlarged to a suitable approximate scale. For display work or report illustrations a system of transparent overlays with coloured symbolization can be produced cheaply by diazo techniques. For thematic mapping the photograph can be reproduced onto scribing film for use as a guide image; the thematic information is scribed in the usual way. A halftone tone version of the aerial photograph becomes the base map and the thematic information is then overprinted in the desired colour. The scale accuracy is normally poor, but this is often off set by the ease with which geographic relationships can be seen.
Every map is a reduction of reality. It is the resulting compression of detail which requires a systematic approach to the selection of information through the process of generalization. Maps, even those at large scales, can not possibly show all the details of an area in their correct relationships. This limitation becomes highly restrictive as scales get smaller. For example, taking information mapped at a scale of 1:25,000 and reducing it to a scale of 1:100,000 will result in a new map occupying only one sixteenth the area of the original. This reduction allows only a limited portion of the original information to be portrayed at the smaller scale. Thus the smaller the scale the greater the amount of generalization required. Successful generalization results in the retention of the distinguishing characteristics of the mapped features so that they are effectively represented despite the restrictions of scale.
The various operations, which together make up the subject of cartographic generalization, are normally discussed under four categories or elements: simplification, classification, symbolization and induction.
The fitting of information to the selected scale of the map and the maintenance, as far as possible, of the essential geographic characteristics of the mapped area are the two primary objectives in mapping. The information must be simplified by judiciously selecting the necessary classes of information to be shown and by reducing its complexities and detail. The information to be discarded or retained is determined by the relative importance of each item, the relation of the data to the map objective and the graphic consequences (to other data, symbols, etc.) of retaining each item.
This is a process of grouping a large, variable mass of information in a relatively orderly and simple manner. For example, fish species could be classified into groupings of genera or families depending on space availability. The number of classes should be fewer and broader on smaller scale products.
This procedure occurs after the processes of simplification and classification have been carried out. Some symbols are highly generalized (the dot) while others are not (latitude and longitude lines). Codes are also used to represent the data and identify its location. Good symbolization enhances the effectiveness of other aspects of generalization; however, it can also infer an unjustifiable degree of precision if derived from poor information. These aspects are discussed later in this section.
This is the process of extending the information content of a map, in areas of limited data availability, by means of logical inference. Isolines drawn through point data measurements are the most common examples. For instance, water temperature and salinity can be inferred from relatively few samples. This process is quite common in the marine environment where sampling is a widely used procedure for observation and measurement. Since extensive inference affects map accuracy, a reliability diagram or statement should be included.
The creative freedom of cartographers is often limited by a number of overlapping restrictions, such as the requirement for economical reproduction, restrictions due to regional geographic shapes, map projections and grids, and allowances for items in the map margin or surround. Nevertheless, there is a definite place for artistic sensibilities and consideration. An attractive map is more likely to be read and in general will be taken more seriously as a professional product.
All major map elements should be placed within the available space in an organized and visually pleasing manner. A formal balance calls for symmetrical balancing of similarly sized and shaped elements in relation to a balance point. This is the approach usually taken by the organizers of series mapping. Typically the title is centred either at the top or the bottom, the latter being visually more stable and preferable. Practically, however, it is often necessary to use the former position. The scale is normally centred at the bottom, and the notes are arranged evenly around the perimeter of the map.
Formal balance is often considered stilted and uninteresting for single maps which are not part of a series. The features shown are unlikely to be symmetrical and the shape of the region governs the locations for the title, legend, scales, etc., in convenient open areas. Thus an informal balance of the elements is required.
In informal balance the visual weight of each element must be considered individually and in relation to the whole design. The various elements must be placed so that there is a general balance. Often a large item such as the title or the legend can be visually offset by two or more smaller elements.
The various possibilities of layout should be first tested in a series of simplified miniature drawings followed by a full-scale dummy which shows outlines of the major elements without detail. It is not possible to create effective designs if major elements must be fitted in at the last moment (Figures 7.2 and 7.3).
In cartography the term compilation means the process of organizing, assembling and fitting together all of the various geographical and thematic data which will be included in the map. The various kinds of data must all be located in their proper planimetric position according to whatever projection system and scale have been chosen. The compilation manuscript becomes the guide for construction of the map and is necessary no matter what technique or equipment is used to create the final product.
The compiling of data may require the use of several information sources including maps at varying scales, published material in both textual and tabular form, field surveys of various kinds, “raw” data derived from aerial photographs, satellite imagery and digital records. Each of the maps may be on different projections and have varying accuracies and scales. Similarly the textual and digital material may exhibit a wide variety of characteristics. It is the task of the cartographer to select appropriate information with which to create the final map, with the intended use of the end product kept firmly in mind. Reliable maps cannot be created from poor or inadequate data sources, regardless of the compilation techniques used.
Figure 7.2 Good and bad solutions to map layout design. (After R.Bertrand and P.J. Oxtoby, 1980)
Figure 7.3 Good and bad solutions to map layout design. (After R. Bertrand and P.J. Oxtoby, 1980)
Surveys of the status of fisheries and marine related information within developing nations often indicate a dearth of such data, at least in a form which can be utilized for management purposes. This state of affairs, invariably due to a lack of manpower, money or expertise, confirms the requirement for fisheries resource mapping with an emphasis on the collection and presentation of marine information in its most basic form. The major source of such information in developing nations is often the fishing community, rather than the research and management agencies associated with industrialized fishing nations. The understandable desire to fund the acquisition of new remotely sensed data (from aircraft and satellites) and to computerize the developing data base should be dependent on the success of data collection and subsequent thematic mapping.
A survey should include the following phases:
i) The formulation of a small project team. Additional expertise or manpower can be called upon as required;
ii) An invitation to selected fisheries personnel to visit an appropriate institution in order to:
a) become familiar with the array of technologies associated
with resource mapping;
b) formulate an acceptable data collection strategy;
c) develop a program itinerary and schedule;
iii) The preparation of large-scale base maps of national waters (inshore) and small-scale base maps of the area as a whole (the 200 mile Extended Economic Zone) on which to collect information;
iv) The field testing of the techniques and logistics of data collection and, accordingly, their refinement;
v) The reviewing of existing data from the sources indicated in Section 7.6.3.
A typical literature review and interview process might include the following marine information categories:
i) Physical features:
a) bathymetry;
b) currents (surface, bottom);
c) temperature;
d) salinity;
e) tidal range;
f) meteorological characteristics;
g) coastal morphology (e.g., beach);
h) near-shore geomorphology;
ii) Type of bottom (habitat):
a) location of coral reefs;
b) sand bottom;
c) mangroves or turtle grass beds;
iii) Resource location by species areas and seasons:
a) reef fish;
b) lobster;
c) conch;
d) turtles;
e) flying fish and other small pelagics (plus baitfish);
f) tunas;
g) other large pelagics (e.g., rainbow runners, kingfish and
billfish);
iv) Fishing areas by species, season, boat and gear type:
a) troll fishing;
b) hand lining;
c) fish traps;
d) seining (purse and shore);
e) foreign fishing vessel sightings (by country), distinguishing
vessels of adjacent countries from distant water fleets;
f) sport fishing;
N.B. Areas fished by nationals, which are outside their area of national jurisdiction, should be indicated.
v) Other marine activities:
a) location of fishermen's communities;
b) number of fishermen, boats and gear types;
c) principal handling and trans-shipment points and harbours;
d) tourist development areas;
e) marine parks and conservation areas;
f) shipping routes;
g) main sources of domestic and industrial pollution;
h) areas designated for aquaculture development;
i) identification of Ciguatera zones.
The identification of information sources for the preparation of a manuscript is a critical phase of any thematic mapping program. In relation to fisheries, jurisdictional conflicts between the numerous national authorities associated with the coastal zone often result in relevant data being housed in the unlikeliest of locations.
Potential sources of information include some or, ideally, all of the following categories:
| i) | published scientific literature; |
| ii) | unpublished scientific material; |
| iii) | library collections of papers on special topics; |
| iv) | government department reports and automated data bases; |
| v) | consultant reports; |
| vi) | commercial bibliographic data bases, e.g., ASFA (Aquatic Sciences and Fisheries Abstracts - an FAO data base); |
| vii) | questionnaire results (sent and received by mail); |
| viii) | interview material; |
| ix) | conventional aerial photograph repository; |
| x) | map collections; |
| xi) | satellite imagery (generally the responsibility of a government or international agency). |
This phase may employ a variety of techniques from relatively simple and inexpensive data gathering activities, such as the deployment of field personnel equipped with coloured felt markers and accurate base maps, to the complex operations associated with data collection from remote sensing platforms (satellites, fixed wing aircraft and helicopters). The information collected can be stored either in the conventional manner on hardcopy maps, or it can be entered into a geographic information system (GIS) and stored in digital form in a computer (refer to Section 14). Utilization of these more advanced techniques is certainly not essential; they should, however, be considered since the more elaborate data collection procedures are becoming commonplace in many developing countries.
The phase of manuscript compilation which involves collection of information in the field is often critical to the success of a marine resource mapping program. It should be carried out sequentially as follows:
The precise format and interview strategy should be prepared in cooperation with fishery officers familiar with the locale, the fisheries and, most importantly, with the fishing community. The format should be simple and unambiguous. A field tested procedure for conducting interviews is as follows:
i) the provision of large-scale base maps of national waters and small-scale base maps of the region as a whole for data collection;
ii) the interviewing of fishermen, fishery officers and other interested and qualified persons (e.g., coast guard and naval personnel, harbour masters, etc.) utilizing the above maps to plot the acquired marine information using felt markers. Sufficient maps should be used to ensure accuracy and comprehension;
iii) the provision of unmarked maps for each person interviewed, identified with his/her name and profession and the name of the interviewer, the date and place. This is important, particularly when interviewing fishermen, to avoid bias caused by seeing the results of previous interviews with other fishermen. The base maps should be filled in, as an integral part of the interview, by the person interviewed, but if need be with the assistance of the interviewer(s). Figure 7.4 is an example of information portrayed by the simple felt marker technique.
The majority of current marine resource information is obtained from those personnel most directly concerned with its exploitation, management and scientific research. The actual interview process will vary according to the individual or group being interviewed:
i) Fishermen: It is advantageous to interview fishermen individually to avoid bias, as previously mentioned. The rationale of the program and the benefits which will be derived from it by the fishing community should be particularly emphasized, as fishermen are generally the most skeptical of the subjects to be interviewed. The considerable effort required to overcome such skepticism and cynicism is most certainly justified by the wealth of information usually obtained. In contrast to many of the species they catch, the fishing community is perhaps the most under-exploited marine resource in the context of information retrieval. This information must, however, be critically assessed in terms of its accuracy;
ii) Fishery officers: When possible, group sessions are recommended for fishery officers. After an initial briefing by a member of the resource mapping team, the officers should be queried about the subject under review. While one or two team members take notes, the other(s) should encourage the officers to draw distribution patterns, etc., on the base maps previously affixed to the walls or tables. The team members must be “animators” and encourage discussion, which pre-supposes a personal knowledge of the local fisheries. Controversy between the officers concerning marine information can often improve the quality of the final product, if the point of controversy can be resolved. The team should attempt to methodically follow the list of topics to be reviewed and at all times record the name of the person who provided particular information, either on the base maps or in the notes. A plentiful supply of coloured markers and unmarked base maps is essential for a successful interview session;
iii) Scientists: It is advisable to interview scientists on an individual basis, partly because of the inherent professional jealousy that results when scientists meet in groups, but also because of the real, and perceived, proprietary nature of their information. A manuscript map, containing information previously obtained from the fishermen and fishery officers, should be the focus of discussion. It will probably elicit criticism, which is required to ensure accurate and verifiable data. It is not possible to elicit much informed opinion, in a short space of time (generally a critical factor), unless a manuscript is available to stimulate and focus the criticism.
Figure 7.4 Example of information presented with the aid of felt markers.
When the information, collected from the above three groups, has been analyzed and collated with other sources of data, another manuscript map should be prepared. At this point it is essential to arrange a “check session” with the key information providers to ensure that their contributions have not been misinterpreted. This session is also a valuable part of the “feedback” process and will increase the confidence of the participants in the worth of the thematic mapping program. The thematic map, as an end product, must be seen to contain reliable and accurate information, otherwise the credibility of the whole program will be lost.
In all cases basic civilities are a prerequisite to a successful interview. Unless these civilities are observed, future efforts to obtain information or cooperation will be jeopardized. These include the following:
i) Prior consultation should take place to ensure that the rationale for the program is clearly understood and, particularly, that the benefits to be derived from the program are identified; the latter will often facilitate cooperation;
ii) The interview format and topics of interest should be circulated in advance. The interview process is unfamiliar to many persons, professional and otherwise, and can be a little forbidding, hence the need to alleviate any fears;
iii) It is essential to establish a precise time and date for the interviews. Unlike other professions, fisheries are often seasonal and are carried out at different times of the day and night. Thus a time should be selected when fishermen and fishery officers are not in the midst of their peak activities, i.e. exhausted personnel are not ideal subjects to interview and the information obtained suffers accordingly;
iv) All arrangements should be confirmed, by letter or by telephone, well in advance of the interview. Another communication a few days prior to the agreed upon date may also help to avoid embarrassment;
v) The location in which the interview is to take place should be chosen with care. Most people feel more relaxed in their home or work environment, rather than in some alien institutional setting. This is particularly true for the fishing community: a fishing boat, dockside or the fisherman's home are ideal settings, assuming prior permission has been arranged;
vi) Awareness of political realities is another prerequisite. The fishing community and personnel from the Department of Fisheries rarely agree on any topic, especially fisheries management and within the fishing community itself there are normally a variety of firmly held opinions. Hence the interviewer must beware of jeopardizing his primary task of collecting information by an injudicious choice of words or reference to a currently volatile topic. Diplomacy is thus essential;
vii) The parties interviewed are naturally aggrieved if they do not see the end results of the program, i.e. a map and/or report. Personal copies are particularly appreciated but the cost of the item is obviously a factor. Acknowledgement of their contribution also is essential, both in the form of a letter of appreciation and in the appropriate acknowledgement section of the end product.
The information and data collected from the numerous sources must now be categorized according to the desired use of the end product, the thematic map(s). The integration of data and its portrayal as thematic information will normally occur within clearly defined categories, i.e. pelagic fisheries, demersal fisheries, habitat, fleet distribution, port infrastructure, etc. Utilization of these various categories, either individually or in combined form, will depend on the map design (refer to Section 6) which in turn will reflect the ultimate use of the map, its management role.
The acceptance of marine resource mapping as a management tool is dependent on the reliability of the contained information. The importance of accurate mapping cannot be overestimated, for instance, in acquaculture leases and development sites, location of artificial reefs and, more generally, coastal zonation and multiple use delineation of nearshore areas. Thus the analysis and evaluation of the categorized data should be thorough and scientifically acceptable. For this reason, all information utilized in the thematic mapping process must be clearly identified with the aid of an “Audit Trail”, to give users of the map(s) the opportunity to check the authenticity of the sources and the credibility of the mapped information. This is particularly important for thematic maps as the original data may have been transformed and integrated with information from other sources.
Under certain circumstances it may be desirable to assess the information in relation to its perceived accuracy. This may be done by graphical means or in accompanying text. Whichever technique is used, it will be open to public scrutiny and may cause considerable concern to the original information providers, particularly if the assessment of their contribution is not complimentary.
The collected information and data to be reviewed and selectively integrated may include not only written material and graphics (maps), but also aerial photography and satellite imagery which will require interpretation. It may be used to update old information or provide new information. The role of aerial photo interpretation, satellite image analysis and geographic information systems (GIS) are considered in general terms in Sections 8 and 14.
Having collected and organized the resource information in the form of a manuscript, it may be necessary to plot this information onto another map at a different scale. There are a variety of manual, mechanical and optical techniques and equipment available to reduce or enlarge a map for this purpose:
i) Grid square or Union Jack method: A grid of squares is drawn on the map which is to receive the information. Increased accuracy can be achieved by drawing the diagonals (hence the term “Union Jack” method). The larger/smaller format is divided up into the same number of squares. Detail is now copied by hand from each square (or triangle) onto its counterpart at the required scale (Figure 7.5). A similar method can be used to transfer detail from aerial photographs to a map;
ii) Similar triangles: This method is particularly well suited for the compilation of linear detail such as contour boundaries, etc. It can be used for both reduction or enlargement. The method is shown in Figure 7.6;
iii) Proportional dividers: These instruments can be valuable for manual compilation; they greatly reduce the amount of time required to perform the two previous procedures. They consist of modified dividers having two equal legs pivoting about a milled wheel attached to a slide piece (Figure 7.7). If the slide piece is moved in the control slot the proportion of one set of legs to the other is changed. Scales are graduated on each of the legs, although these are only an approximate guide. Exacting scales are usually determined after a few minutes of trial and error. The variable proportion makes it possible to measure a distance on one map with one end of the dividers, turn the instrument over and plot onto the manuscript directly with the other end. Most proportional dividers have scales graduated for planimetry on one side and circles on the other, increasing their versatility;
iv) Parallelogram pantographs: These various devices make use of simple geometric ratios, based on the properties of parallel lines, to change scale. They consist of a system of rigid arms, hinged or sliding, forming a parallelogram with extensions. At certain points are mounted a pivot (which does not move), a tracing point and a drawing pencil. When these three loci are adjusted correctly for the required scale change, and the tracing point is used to trace the original map, the pencil draws the map at the new scale (Figure 7.8);
v) Photography (refer to Section 12): The only serious problem with this technique is ensuring that the correct scale change has been obtained. This can be checked with the grid square method;
vi) Specialized projectors: A map can be projected, enlarged or reduced, as required, onto paper laid over a glass screen. Once the correct setting is obtained (check with the grid square method) the lines of the map are drawn on the paper. Examples of these projectors include:
Figure 7.5 Grid square method for enlargement or reduction. (After C.L. Blair and R.I. Simpson, 1978)
Figure 7.6 Triangle method for enlargement or reduction. (After P.J. Oxtoby and A. Brown, 1976)
Figure 7.7 Proportional dividers. (After International Cartographic Association, 1984)
Figure 7.8 Parallelogram pantograph. (After H. Graham, 1968)
a) Grant projector;
b) Klimsch Antiskop;
c) Map O'Graph;
d) Kail projector;
vii) Slide projector or epidiascope (overhead projector): These are crude methods for scale changing and only enlargements can be easily produced. A slide or transparency of the original must be available for projection. To avoid distortion, the axis of projection and the paper onto which the map is to be drawn, must be at right angles. Once again, the grid square method is an appropriate method to check correct scale change. It is possible to reduce an image with an overhead projector if the subject is brightly lit in a darkened room. The stage of the projector can be used as a small tracing table, and in this case, no transparency is necessary.
