Chapter 1: Introduction to Thematic Mapping

The Realm of Maps

• Professional cartographers think of maps as vehicles for the transmission of knowledge and for analysis for discovery

• The map defined

  • A map is a graphic representation of the milieu

    • Milieu include all aspects of the cultural and physical environment

  • A map is also described as ‘a model of reality’

• The most basic map distinctions in modern cartography:

  • Tangible (real) vs. Virtual

    • Tangible map: printed hard copy

    • Virtual map: viewable but without a physical or tangible reality- computer monitor display or projected display in a classroom

• Cf. mental maps:

  • defined as a mental image that have spatial attributes

  • Are developed in our minds over time by the accumulation of many sensory inputs

  • Can be either tangible or virtual

    • e.g. what is a mental map of your home town? Your mental map may be different from your brother’s or sister’s because everybody has their own perception even about the same object

What is Cartography

• Definition of mapmaking or mapping

  • refers to all of the processes of producing a map, whether the person is collecting data, performing the design of the map, or preparing the map for distribution as a hardcopy or for the web

  • ‘ the process of designing, compiling, and producing maps’

• Definition of Cartography

  • Cartography is viewed as broader than mapping

  • Defined as the study of the artistic and scientific foundations of mapmaking

Geographic Cartography

• Geographic cartography, although a part of all cartography, should be defined a bit further because it is a main tool and a product of a geographer

• Is defined as a subfield that requires:

  • Understanding of the spatial perspective of the physical environment

  • Understanding of areal relationship

  • Skills in map projection selection

  • Knowledge of the map scale

  • to be adapt at map reading (interpretation)

Kinds of Maps

General Purpose Maps vs. Thematic Maps

• General Purpose Map:

  • Also called a reference map

  • displays a variety of features of the world or a portion of it

    • ex. coastlines, water features, political boundaries, roads, cities, and other similar objects

  • Includes topographic maps, maps of countries and states, atlas maps, etc.

    • topographic map: general-use maps that show elevation (contour lines), hydrography, geographic place names, and a variety of cultural features

• Thematic Maps

  • Also called a special-purpose, single-topic, or statistical map

  • Defined as “A map designed to demonstrate particular features or concepts”

    • Note: Topographic maps show more details of elevation, but are still considered a general purpose map because it includes other feature as well as elevation.

  • Two subdivisions of thematic maps: Qualitative vs. Quantitative

    • Qualitative

      • Show the spatial distribution or location of a single theme of nominal data

      • No quantitative (numbers) information is presented

        • ex. maps of ecoregions, geology, soil types, and land use/land cover maps

    • Quantitative

      • Display the spatial aspects of numerical data

      • The principal operation is in the transformation of tabular data into the spatial format of the map

      • The numerical values are generalized with symbols, so the map does not usually show exact amounts

      • Common Quantitative Thematic Maps

        • Choropleth, Dot, Proportional symbol, Isarithmic (or contour map), Value-by area cartogram, Flow

Types of Quantitative Thematic Maps

• Choropleth map: shows data collected in enumeration units

  • Each unit in a map, such as a county, is shaded according to a variable or attribute, such as population density

• Dot map: shows variations in spatial density

  • One dot represents so many units of some commodity

• Proportional symbol map: has symbols that are scaled to values at points

  • The point may be an actual point feature, such as a city

  • The point may also derived from an area unit, such as the center of state

• Isarithmic map: shows 3-D continuous volumes, such as elevation, temperature, or precipitation

  • Isarithms (isolines) connect points or places of equal values

• Value-by-Area Cartogram:

  • The enumeration units’ area values are replaced by the variable being represented, often creating a very striking appearance in the map

• Flow map: show linear movement between places

  • The lines’ thickness and/or color indicate the magnitude of the flow or movement

Components of the Thematic Map

• Three important component

  • A geographic or base map: provides basic locational information to which the thematic overlay can be related

  • A thematic overlay: theme that will be displayed

  • A set of ancillary map elements: titles, legends, compilation credits, neat lines, and others

    • Titles: the main map title and/or subtitles

    • Legends: help readers correctly interpret symbols, data ranges, etc.

    • Compilation credits (source statements): acknowledge the source for any data used in the map; they may include the map authorship

    • Neat lines: are usually a thin, unobtrusive line that surrounds the mapped area

Map Scale

• Map scale: a ration of map distance to earth distance

• Large-scale map vs. Small-scale map

  • Large-scale map: shows small portions of the Earth’s surface

    • Therefore, detailed information is shown (Large in detail)

  • Small-scale map: shows large area

    • Therefore, limited detail or generalized situations can be displayed on the map (small in detail)

• Another important consequence of scale selection is its impact on symbolization

  • At large scales, the outlie and area of a city may be shown in proportion to its actual size- that is, it may occupy areas on the map proportional to the city’s area

  • At smaller scales, whole cities may be represented by a single dot having no size relation to the city’s real size

Modern View of Map Communication

• Traditionally, maps have been used as communication tools using visualization → emphasis on communication

• Now, maps are seen as tools in finding patterns and relationships among mapped data, not simply for the communication of ideas to others → more emphasis on ‘analysis’

Cartographic Communication: Three Parts

• Map author: someone who wishes to convey a spatial message (may or may not be a mapmaker (=cartographer))

• Cartographer (=mapmaker): a trained scientist who creates a map using cartographic abstraction (generalization)

• Map reader (=map percipient): an end user who gains a spatial knowledge by looking at a map with t he following three steps in order

  • Map reading: map readers see what is displayed and how the mapmaker did it

  • Map analysis: map readers begin to see different patterns on a closer inspection

  • Map interpretation: finally map readers are able to explain what these patterns show

Cartographic Abstraction (Generalization)

• Cartographic Abstraction (Generalization)

  • Is transforming unmapped data into map form and selecting and organizing the information necessary to develop the user’s understanding of the concepts

  • There are four elements:

    • Selection

    • Classification

    • Simplification

    • Symbolization

Four Elements of Cartographic Abstraction (Generalization)

• Selection

  • Involves an early decision regarding the geographic space to be mapped, map scale, map projection and aspect, which data variable are appropriate for the map’s purpose, and any data gathering or sampling methods that must be employed

• Classification

  • Is a process in which objects are placed in groups having identical or similar features

  • The individuality and details of each element is lost

  • Reduces the complexity of the map image, helps to organize the mapped information, and thus enhances communication

    • e.g. map of wheat area, corn area, rice area, and millet area vs. map of crop area (four different areas vs. on simple area)

• Simplification

  • e.g. A path (a road) can be straightened if the purpose of a map is simply to show connectivity between two points, not to illustrate the road's precise locational features

• Symbolization

  • Is required because it is not possible to create a reduced image of the real world without devising a set of marks (symbols) that stand for real-world things

    • Two major class of symbols: Replicative vs Abstract

      • Replicative symbols: those that are designed to look like their real-world counterparts, such as coastlines, trees, railroads, house, and cars

      • Abstract symbols: usually take the form of geographic shapes, such as circles, squares, and triangles; for this type of symbols, a detailed legend is required

        • Whether replicative or abstract symbols are used also depends on the map scale: at smaller scales, it is virtually impossible to represent geographical features

Difference between Cartography and GIS

• GIS (Geographic Information Systems)

  • Cartography plus a computer0based system with data management and the ability of spatial analysis

Ethics in Cartography

• Because maps are made by humans, they may contain purposeful errors (lies) or errors of oversight and poor judgement or both as a consequence

• There are no governing bodies charged with guiding the ethical practices of thematic mappers

• Thus, the intent, honesty, and credentials of each cartographer must be dealt with on an individual basis and his or her reputation must be considered