Session 01 : Definitions and concepts
Steps in the Graphic Processing of Information and Creation of a Thematic Map
1.1. Theory and Cartographic Design (scale, generalization, types of layout)
1.2. Processing of Statistical Data (discretization)
1.3. Types of Data (qualitative/quantitative data) and Graphic Semiology
1.
cartography:
Cartography can
be defined as the practice or study of map making. To further explain, the art
of cartography and therefore the work of the cartographer allows us to
understand the geographic landscape around us through a principle of
mathematical scale, graphical representation and associated symbology.
Cartography has been around for thousands of years and much has been written
about the history of cartography and the complexities of map projections,
however in this short blog we focus on defining the modern cartographic process
from initial needs assessment to delivery of the finished map in the agreed
format.
2. Map : The map is the science, technology and
art of cartographic mapping and using maps (Miljenko Lapaine 2021).
2.1.Types of maps
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Base
map
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Thematic
map
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Analytic
map
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Syntithic
map
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Geologic
Basemap 
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Topographic
Basemap 
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2.2.
Map’s elementes
The frame
of the map: makes
it possible to delimit the information outside it from that which is inside.
Alle map has principal elements:
2.3.
Topographic basemap What can I learn
using these maps?
Outside the frame: All information placed outside the
frame of the map is for convenience and allows for easier reading of the
map. which the map was designed.
a- Sheet
number: allowing
it to be placed in an assembly table.
b. Orientation (North, South):
c. North Arrow (Geographic North and Magnetic North):
Most topographic maps have an arrow showing north. There may be a difference
between geographic north (true north) and magnetic north, which can vary
depending on the location and time.
D. Grid: Geographic
coordinates (latitude and longitude) or a UTM (Universal Transverse Mercator) grid
can help you pinpoint exact locations on the map. Coordinate network: allowing
to locate all the facts in latitude (angle of the vertical of a place with the
plane of the Equator) and in longitude (angle formed by the plane of the
Meridian of the place with that of the Meridian taken as origin).
On the map, specification of geographic coordinates and cartographic
coordinates (LAMBERT coordinates/ kilometric grid) Two (02) coordinate networks
are commonly used:
*-The best known, the geographical coordinates counted from the Equator
and a Prime Meridian (most often the Greenwich Meridian). They are divided into
Grades and
Tenths.
*- for
some maps, the cartographic coordinates have been added which form a kilometric
grid expressed in numbers increasing from west to east and from south to south. Orientation system: a map is oriented
and a direction is expressed by an angle counted from the North. Three (03)
North are used and shown on the maps on their right margin:
* Cartographic
North (or North Lambert) indicated by “y”
* The
geographic (or astronomical) North indicated by “N.G”
* the
magnetic North indicated by “N.M”. It is
indicated by the magnetic needle and forming an angle or magnetic declination
which varies with time in relation to geographic North.
e. Legend
and Scale:
ü
Legend: This is a key part of the map that
explains the symbols and colors used. Every feature (building, watercourse,
forest) has a unique symbol.
Scale: The scale, usually expressed as a ratio
(e.g., 1:25,000), tells you how much the map has been reduced. A scale of
1:25,000 means that 1 cm on the map equals 250 meters in reality.
Reduction
scale: Numerical scale and graphic scale. The scale of the map is the ratio
between the lengths measured on the map and their real equivalent on the
ground. It is expressed by a fraction whose numerator is always the number 1
(it expresses the unit, whatever it is - mm, cm dm, m -) and the denominator a
number which is the divisor of the real lengths and makes it possible to obtain
the reduced lengths.
Examples:
- on the
1/50,000 map, the cm for example represents 50,000 cm on the ground, i.e. 500m
- on the
1/200,000 map, the cm = 200,000 cm or 2000m, or even 2 km.
-A map is
said to be on a large scale when the reduction it allows is small (ex:
1/50,000.1/25,000) and therefore the denominator is small-On the other hand, it
is on a small scale when the reduction is large (ex: 1/500,000, 1/1,000,000),
and therefore the denominator is large.
-The
scale is indicated at the bottom of the map, and is expressed by the fraction
(numerical scale) and by a graphic scale divided into km for the right part, in
hm for the left part or heel.
The
scales most commonly used vary according to the country and according to the
purpose to which the map must respond; also, once the goal is defined, it is
necessary to decide on the content of the map and therefore on the best scale
so that the characteristics necessary for a general inventory of a territory
can be represented.
-
Establishing topographic maps at different scales serves different purposes.
Maps at
1/50,000 are the most used but when you want more detail, we use 1/25,000 and
when you want to see a wider view, maps at 1/100,000 or 1/200,000 are more
appropriate.
* The
choice of map scale depends on:
The small
scale shows the largest elements belonging to the physical environment (i.e.
for a physical study, the choice of the small scale is essential).
On the
other hand, for a study of the organization of space, only the large scale
gives information with sufficient detail and greater precision in the location
of the latter.
From the
small to the large scale, the characteristics of the physical environment fade
to the detriment of those of the organization of space, the great detail gives
way to a multitude of details which bring out more the action of man. on its
middle.
*The
arable land is left blank and the best document to consult to find out about
this point is aerial photos
g.
Source:
designating by which service or organization the card was established.
h. Date: date of creation of the map
2.
CLASSIFICATION DES CARTES
"Il existe
plusieurs types de classification. Celle retenue ici repose sur la notion de
contenu des cartes et retient la distinction entre cartes topographiques et
cartes thématiques.
2.1. les
cartes topographiques sont celles sur lesquelles figurent essentiellement les résultats
d’observations directes concernant la position en longitude et en latitude, la
position altimétrique, la forme, l dimension et l’identification des phénomènes
concrets permanents existant à la surface du sol.. Les cartes topographiques
sont établies sur la base de conventions, identiques pour l’ensemble des cartes
et à des échelles bien précises.
Définition
du Comité Français de Cartographie : " une carte topographique est une
représentation exacte et détaillée de la surface terrestre, concernant la
position, la forme, les dimensions et l’identification des accidents du
terrain, ainsi que des objets qui s’y trouvent en permanence.
Le but de
ces cartes est essentiellement pratique. La nécessité d’y retrouver tous les
éléments visibles du paysage, et de pouvoir y effectuer des mesures de
directions, de distances, de dénivellations et de surfaces, exige une échelle
appropriée.
Pour les cartes topographiques, les
échelles sont arrêtées :
- Les cartes
à grande échelle (de 1/10 000 à 1/25 000),
- Les cartes
à moyenne échelle (de 1/50 000 à 1/100 000), - Les cartes à petite échelle (au
1/200 000).
Pour les
cartes à des échelles supérieures (1/1 000, 1/2 000, 1/5 000), on parlera de
plans et pour les cartes à des échelles inférieures (1/250 000, 1/500 000, 1/1
000 000, ), on emploiera le terme de cartes générales." licence fondamentale en géographie (FSHS
2.2. Les
cartes thématiques : représentent sur un fond repère un thème particulier. Il
existe une infinité de cartes thématiques et deux cartes traitant du même thème
peuvent être très différentes d’un point de vue graphique. Il n’existe pas de
conventions régissant les représentations thématiques, mais uniquement des
outils graphiques permettant de faire passer au mieux un message. De même, il
existe une infinité d’échelles.
La notion de
carte thématique est récente et date des années 1950.
3.Map Creation Process:
Creating a map involves several stages, as outlined in the Fundamental License in Geography curriculum from the Faculty of Humanities and Social Sciences (FSHS). The process begins with Topographic Surveying, where all landscape features are cataloged according to precise latitude, longitude, and altitude coordinates. Methods for this step include ground surveying, setting up a geodetic network, and interpreting aerial photographs or satellite images.
The next phase, Cartographic Representation, requires organizing and processing collected data to prepare it for presentation on a suitable medium. For instance, aerial photographs are assembled into a stereoscopic view with specialized devices and plotters to render the terrain's relief, which ultimately enables map tracing. Similarly, satellite data is transmitted directly to computerized databases for processing, much like aerial imagery.
Finally, Cartographic Publishing standardizes the map presentation, adhering to conventions regarding orientation, symbols, colors, textures, line thicknesses, and labels to ensure clarity and consistency (FSHS).
1.2. Processing of Statistical Data (discretization)Discretization, a fundamental process in the preparation of statistical data for thematic cartography, involves dividing continuous datasets into distinct classes or intervals to improve data interpretability and visual presentation. By simplifying continuous data into manageable categories, discretization facilitates meaningful comparisons across geographic regions, allowing cartographers to emphasize spatial patterns without overwhelming the map viewer with intricate data details (Slocum et al., 2008).
Several standard methods of discretization are widely employed in cartography, each with unique implications for data interpretation. The equal interval method divides the data range into equally spaced intervals, offering simplicity but sometimes obscuring regional variability in datasets with significant outliers (Robinson & Petchenik, 1984). In contrast, quantile classification allocates an equal number of data points per interval, effectively highlighting rank or relative standing among categories but occasionally distorting differences between class values (Kraak & Ormeling, 2020). Meanwhile, natural breaks (Jenks) attempts to minimize intra-class variance by identifying natural clusters within the data, making it well-suited for datasets with pronounced gaps or clusters, such as income disparities across urban areas (Dent et al., 2009). Lastly, the standard deviation method classifies data based on statistical deviation from the mean, enhancing the detection of values significantly above or below average, which is particularly effective for datasets like income distributions where outliers are meaningful (Brewer, 2016).
Each discretization method inherently shapes the viewer’s interpretation of spatial data patterns, as highlighted by Monmonier’s work on map design ethics, which emphasizes the responsibility of cartographers to choose classification techniques that balance clarity and representational honesty (Monmonier, 1996). Consequently, understanding the statistical and visual implications of discretization is essential for producing accurate and ethically sound thematic maps.
1.3. Types of Data (qualitative/quantitative data) and Graphic Semiology
In cartography, understanding data types—qualitative and quantitative—is essential for selecting appropriate graphic semiology methods to represent spatial information effectively. Qualitative data describes categories or classes without inherent numerical value, such as land use types (e.g., residential, industrial, agricultural) or soil classifications. This type of data requires distinct visual markers like color, shape, or texture, allowing viewers to easily differentiate between categories without inferring magnitude (MacEachren, 1995). Conversely, quantitative data encompasses measurable numerical values, such as population density or elevation levels, and is often represented through proportional symbols, graduated colors, or intensity to convey magnitude and variation within the mapped region (Bertin, 1983).
Graphic semiology, a system of visual variables developed for effective map communication, supports the accurate portrayal of both qualitative and quantitative data. Graphic variables—such as size, color, orientation, and value—play a critical role in translating data into visual forms that the viewer can intuitively interpret. For example, size can represent quantity in quantitative maps, making it a suitable choice for population symbols, while color and texture are often employed in qualitative maps to differentiate distinct categories like vegetation types or political regions (Brewer, 2016). Properly matched graphic semiology to data type ensures not only readability but also enhances the viewer's capacity to interpret spatial relationships and patterns, a core objective of thematic cartography (Tyner, 2010).
The field’s commitment to accurately conveying geographic information through semiology underscores the need for cartographers to understand the subtleties of both data types and the visual tools at their disposal. As Bertin’s foundational work in graphic semiology emphasizes, effective map design hinges on an understanding of how visual variables can best represent various data structures, fostering maps that are both informative and visually engaging (Bertin, 1983).
Bertin, J. (1983). Semiology of Graphics: Diagrams, Networks, Maps. University of Wisconsin Press.
Brewer, C. A. (2016). Designing Better Maps: A Guide for GIS Users. Esri Press.
MacEachren, A. M. (1995). How Maps Work: Representation, Visualization, and Design. Guilford Press.
Tyner, J. A. (2010). Principles of Map Design. Guilford Press.
