G. LAMARQUE *
(*) G. Lamarque, Cartographie Section I.E.M.V.T.
Purpose of mapping - two-fold option
Criteria to be strictly followed in rangeland cartography
Homogeneity of presentation
Evolution of the presentation of rangeland cartography at I.E.M.V.T. over the past 14 years
Conclusions and wishes
The development of animal production in the tropical zone requires the use of increasingly precise cartography in drawing up the pasture inventory essential for the success of this development.
Documents should be made which are simple and directly available to the breeders, and contain a reservoir of data for research workers in botany and phyto-sociology.
Uniformity in the presentation of maps of pastureland will facilitate reading for the users and thus allow them to make maximum use of the information contained in such documents.
It is necessary that this unifying process be developed in the years to come, in spite of certain problems; these are in fact in the process of being solved.
For its part, I.E.M.V.T. is continuing the work it began 14 years ago towards the achievement of standardised production and immediate utilisation.
Taking into consideration the observations of users, it hopes to further improve its maps of pastureland so that they may fulfil numerous different purposes.
a) Immediate use.
b) Applied research.
This is a question of describing, for practical purposes, the potential productivity of a region within strict limits, using a topographical foundation which already exists or which has to be developed.
The drawing up of a cartographic document begins in the first instance with a plotting model of the different areas of rangeland. Thus the surveyor replies to the grazier's question: "How many hectares have I that can be grazed in the rainy season, in the dry season, and all year round?"
Presentation of the map should thus provide the most detailed information possible concerning:
2) Identification of the rangeland;
3) Use of this rangeland according to season;
4) Animal carrying capacity, per hectare;
5) Recent modifications in the means of access location of villages, crops, and all the other pedological, geomorphological and anthropical factors which may exert an influence on livestock.
With regard to the second option the map should give some indication of the ecology of plant species by means of a key presented in the form of a classification of different formations from the driest to the most humid.
Each unit of pasture is distinguished by its own colour and its own symbol (code letter). The text should be a concise abstract of the appropriate paragraph of the report drafted by the rangeland specialist, of which the map is an illustration.
1) Achieve perfect legibility for as much information as possible.
2) Arrange the subject matter in order of priority, keeping in mind the importance of the basic topographical description.
3) Ensure the best arrangement of keys, tables "plans de situation", etc., which determine the use of the map.
4) Choose well-differentiated colours, preferably treated to be able to resist the effect of exposure to the sun, since maps are inevitably used in such conditions in tropical zones.
5) Seek homogeneity of presentation with regard to conventional signs, colours, general drafting and the drafting of formats, which should ideally be standardised, according to scale, in order to facilitate direct use *.(*) We should consider the square degree as basic unit.
The conditions described above are on the whole characteristic of thematic maps generally, but it is useful to call them to mind since they determine the quality of the cartographic document.
It is important that the user of a map be able to obtain instantly a certain amount of basic essential information. For example:
1) Identification of the zone under consideration (Sahelian, Soudanian, etc);
2) Overall value of the region studied (inclined to be good or bad);
3) Immediate identification of the best pastureland, etc.
Information cannot be immediately obtained from documents unless there has been standardisation of presentation.
If maps are always given the same appearance, they will become familiar to the user, who will hence obtain optimum use without tedious research.
Many obstacles exist in the standardisation of rangeland cartography:
1) The lack of international rules governing publications;
2) The disparity between research objectives (ranching, rangeland feasibility studies at regional or state level, studies of anthropical phenomena, over-grazing, etc.), influencing choice of scale;
3) The disparity of financial and technical resources between societies and between states;
4) Certain technical problems connected with different printing methods. Examples:- lack of stability between two offset editions,
- differences between offset and other printing processes;
5) Insufficient distribution of cartographic documents, only a small number of copies are ever made and the requesting authority retains publication rights.
This leads to a situation where individual organizations have little knowledge of production in general. It is evident that work must be done with regard to the different aspects of technology, finance, and of co-ordination and research in cartographic reproduction.
Before the creation at the beginning of 1964, of its own department of cartography, I.E.M.V.T. carried out several studies:
1) Ouadi Rime (Gillet 1961);
2) Le Hodh (Mauritania, Boudet - Duverger 1961);
3) Kaedi-M'Bout (Mauritania, Mosnier 1961);
4) Toumodi (Ivory Coast, Boudet 1963);
5) Ranch Nord-Sanam (Niger, Peyre de Fabrègues 1963).
In 1963, an article* on rangeland cartography from aerial photographs, written by G. Boudet - F. Baeyens established the necessary foundations for the first publications of the I.E.M.V.T. department, which began operations the following year.
(*) Livestock Reviews of I.E.M.V.T.
The first document published was a "ranch map" in 1/50,000 scale of the Gomoko region in the Central African Republic (G. Boudet - J. Andru). This publication was a modest presentation in 2 colours; in choosing the colour red for the rangeland component it was not the intention of the authors to symbolise any ecological category; their aim was simply to define clearly the principal areas of rangeland.
The study of livestock in the Western zone of the Central African Republic in 1/200,000 scale (J.C. Bille) subsequently carried out, made use of 5 colours and included a detailed area in 1/50,000 scale around Sarki. The aim of this operation was to show up considerable over-grazing. It required the use of conventional signs overprinted in black.
b) Choice of colours
In 1966 I.E.M.V.T. took the decision to adopt the recommendations of U.N.E.S.C.O. in the choice of colours. The work of Professor Gaussen (map of the world's vegetation cover - bioclimatic map of the Mediterranean basin - map of the vegetation of the basin) was used as the reference source for colour use in reflecting the ecological categories of vegetation. These principles were applied at I.E.M.V.T. for the first time on the occasion of the issue of the document on North-Gouré in 1/100,000 scale (Peyre de Fabrègues), for which the dominant colour was chosen from the orange range, tropical Sahelian zone colouring. Yellow was retained for valleys and certain mauves for low-lying land.
From this publication onwards, the cartography department of the Veterinary Institute has undertaken to respect the U.N.E.S.C.O. conventions ** and has achieved standardisation with respect to choice of colours - thus allowing a document to be easily placed in relation to broad climatic zones.
(**) Blue for hydromorphic classes, red for sub-Sahara rangeland. problem, for the user, of the immediate identification of the best pasturelands. c) Evolution in the presentation of conventional signs
On the North-Gouré map and on certain preceding ones, the values of different pasturelands were recorded on the main body of the map by means of the overprinting in black of hachures slanted in various directions. This simple process is inconvenient in that it impedes the legibility of the map where the basic topographical description is of particular importance. Research into presentation is being carried out at the moment and certain tests are being made in order to find a solution to the major problem, for the user, of the identification of the best pasturelands.
c) Evolution in the presentation of conventional signs
In the first publications there existed only keys relating to ecological categories, which consisted of pedological and geomorphological information for each formation and the name of the two or three dominant species. The rangeland was classified from the driest to the most humid and from good to bad according to the seasons.
On the occasion of the publication of the map of Dallol - Maouri (1/200,000), G. Boudet included next to the ecological key a presentation of the areas of rangeland according to their value over the seasons.
This concept has been preserved and perfected in subsequent publications. At this time I.E.M.V.T. maps consist of:
- a key to ecological categories,
- a classification of the rangeland with information concerning forage value and animal carrying capacities,
- a table listing the most frequently occurring species.
As may be easily noted, the above type of presentation takes into account the twofold concern for use and applied research.
It is necessary to work to ensure that rangeland maps are not just descriptive "snapshots" of one particular epoch, but on the contrary are documents providing information concerning the evolution of rangeland which maintains a certain rate of stocking for a given period of time. To achieve such an aim it must be possible to carry out fresh work on documents which have already been published and to bring them up to date after several years.
It would be beneficial if in future planning a support mission were provided in order to bring up to date basic maps. This operation, which would be very informative, would certainly also be very profitable for livestock development and henceforward, in many cases, indispensable.
It is also important that in the future organisations responsible for research should establish good lines of communication with each other. It would be desirable to carry out the exchange of documents and to enable specialists to meet periodically to try to identify common methods of expression.
We consider this to be one of the aims of the seminar. We sincerely hope that it will be achieved, and that further working meetings for the improvement of cartography will take place; the mission of such meetings would be the description of a rapidly and constantly evolving phenomenon.
COMPOSITION BOTANIQUE DES PATURAGES
TYPES DE PATURAGES ET CAPACITE DE CHARGE