GIS and CARTOGRAPHY

VICKI DRAKE

Department of Earth Science

Santa Monica College

GIS and Cartography

•In general, output from GIS does not have to be a map

•Many GIS are designed with poor map output capabilities

•Text output may be more important than a map for analysis reporting

•However, much GIS output is in the form of hard copy maps or graphic displays

•Design of graphic output is critical to effective use of GIS analysis

GIS and Cartography

•Graphic output from GIS usually poorly designed

–Colors used randomly without appropriate or conventional scaling as used in cartography

•The greater capability of a screen display introduces new challenges from standard paper map display

•For GIS, the graphic output should show

–Features approximately symbolized or labeled

–Objects computed by the GIS (buffer zone, I.e.)

–Relationships between features

GIS and Cartography

•What are some of the concerns regarding using the screen display as a GIS output?

•The screen, in general, is smaller with a lower resolution than a printed or plotted map

–The screen is, however, more flexible allowing for “zoom, pan, interaction, use of color”

•A hard copy map displays all the information necessary to satisfy a user needs

–An interactive screen displays limited information, but provides for access to more information with a ‘mouse click’.

GIS and Cartography

•Cartographic traditions are fundamentally important to GIS

•Maps are the main source of data for GIS and GIS has roots in the analysis of information on maps

•GIS output is most often in the form of a map, and as such, can benefit from principles of cartographic design developed in cartography regarding:

–Graphical excellence

–Principles of map design

•Remember –computers do not make good or bad maps – cartographers do!

GIS and Cartography

•Maps are a means of recording and communicating two kinds of information about the natural world, of society and culture

–Location (mathematically)

–Spatial characteristics of the location

•Maps, according to the International Cartographic Association, are …”a representation, to scale and on a flat medium, of a selection of material or abstract features on the surface of the Earth…”

GIS and Cartography

•Production of a map requires:

–The selection of features in the real world to include

–Classification of the selected features

–Simplification of complex lines (like coastlines, rivers)

–Exaggeration of included features that are too small to show at scale of the map

–Symbolization of the different classes of the selected features

GIS and Cartography

•Maps have value in three ways

• (1) As a means of recording and storing information

–Plat, parcel, cadastral maps record property

–Census maps record population

–Infrastructure or utilities maps record water, power, telephone and transportation lines

–Location of USGS water-quality test sites in Wisconsin

GIS and Cartography

•(2) Analyzing locational distributions and spatial patterns

–Maps visually allow recognition of spatial distributions and relationships - patterns and spatial processes can be easily determined and analyzed

–Environmental factors affecting poverty in Africa, by Christine Byer, George Mason

GIS and Cartography

•(3) Maps are a method of presenting information and communicating findings

–Findings that are difficult to express verbally are more easily conveyed through a map.

–Maps can be used to convince or persuade

–The Rise and Fall of Mesoamerica by Chad Shuey, George Mason University

GIS and Cartography

•Maps, then, can be viewed as a form of visual communication – the language being that of describing spatial relationships

•Maps are symbolic representations of reality – a ‘generalization’ or ‘abstraction’ even

•Simplification of the real world is inevitable as symbols are used to stand for ‘real objects’

GIS and Cartography

•In practice, there are two types of maps:

•Topographic Map – a reference tool, showing outlines of selected natural and man-made features on the Earth

•Thematic Map – a communication tool, showing distribution of geographical concepts such as population, climate, land use, etc.

GIS and Cartography

•In GIS, there are several important thematic maps

•Choropleth map – using “reporting zones” to show data (census tracts, for example)

–Zone boundaries independent from data

•Area Class map – showing zones of constant attributes (vegetation, soil type, or forest species)

–Zone boundaries determined by distribution of mapped attribute data

•Isopleth map – continuous surface maps connecting ‘isolines’ (topographic contours, precipitation, temperature or air pressure data)

–Phenomena varies smoothly across map surface

GIS and Cartography

•The measure of a good map is how well it conveys information

•Questions to be addressed in the making of a map:

•What is the goal of this map?

•Who is the intended user of this map?

•Where and how will this map be used?

•What data is available for the composition of the map?

•What resources are available (time, equipment, etc.)?

GIS and Cartography

•Questions relating to the form, layout and composition of a map are just as important as those of the ‘message, audience and context’

•The final size, proportions and the media used for production must be considered

•The concept of ‘scale’ of a map must also be considered.

GIS and Cartography

•Scale of a map is the ratio between distances on the map and corresponding distances in the real world

•“Small scale” and “large scale” are often confused

–Large-scale maps show great details, small features (large representative fraction: 1:10,000)

–Small-scale maps show little detail, large features (small representative fraction: 1:250,000)

•Scale not only controls how features are shown, but what features are shown

–For example, a 1:2,500 map will show individual houses, while a 1:100,000 map will not

GIS and Cartography

•The amount of detail included is dependent on the scale at which the map is produced

–A small scale map must be more generalized

–A large scale map will be less generalized

GIS and Cartography

•Basic Map Elements – Information commonly needed by a map reader

•Title, scale, legend, body of map, north arrow, cartographer, neatline, date of production, projection used, etc. are examples of map elements

GIS and Cartography

•Each map element is given an importance and priority within the overall map design.

•The most important elements are featured in more prominent positions, occupying a larger portion of the entire map.

•Once the ‘hierarchy’ and arrangement of the elements is established, the overall balance within the map frame needs to be considered.

GIS and Cartography

•Creating a map layout is as much an art form as a science.

•Experimentation with possible layouts, and rearranging the elements is needed to achieve an effective final map layout.

•There should be a good reason for each element placed on the map, and for its composition and position

•The slogan “less is more” is a good rule to follow. Too much detail or too complex a layout is confusing and works against effective communication

GIS and Cartography

•The use of symbols to represent location, direction, distance, movement, etc is how cartographers represent the real world on a map (into points, lines, areas)

•A variety of visual resources are used and employed to draw attention to map features, or to stress particularly important information

• The “Cartographer’s Palette” demonstrates some of the symbols used (from Jacques Bertin’s The Semiology of Graphics, (1983))

GIS and Cartography

•The symbology used varies greatly depending on the nature of the phenomena being mapped

•Four levels of measurement are distinguished to describe real-world phenomena

–Nominal Data – information grouped into categories based on qualitative considerations (a road different from a river)

–Ordinal Data – information grouped by rank on the basis of a quantitative measures (small, medium, large)

–Interval Data – information arranged along a standard scale, beginning at an arbitrary zero, zero does not mean no data (temperature, for example)

–Ratio Data – information arranged along a scale, but scale begins at non-arbitrary zero point (no feature/data at this zero)

GIS and Cartography

•Add text to a map is a demanding task.

•The content and the form of the text is of great concern to the cartographer.

•It is possible that the verbal content of a map is one of the powerful differences between a high-quality, professional map and an ineffective confusing map.

GIS and Cartography

•Special attention must be paid to the orientation of text with respect to the features being labeled.

•Point features – lettering ‘points’ to the feature, but avoid lettering over boundaries

GIS and Cartography

•Linear features – lettering shows the features, but should not overlap map contents, and should reflect hierarchy of features by the use of different font sizes

•Area features – letter occupies the area itself but may be connected to the feature by an arrow

•Arrangement of the letters can convey subtle distinctions. Lettering pertinent to the map theme may be aligned with the map frame, whereas lettering describing background features is usually aligned with the graticule (latitude/longitude grid of map)

GIS and Cartography

•Foreground-background relationships expect that the most important map information will be displayed in the foreground to ‘catch’ the map reader’s attention

•Details, then, will be assigned to the ‘background’ to make the map less confusing and more intelligible.

•The use of color, value and patterning are ways in which cartographers can help resolve ambiguities

GIS and Cartography

SMC 2000-2001