DATA VISUALIZATION GABRIEL PARODI STUDY MATERIAL: PRINCIPLES OF GEOGRAPHIC INFORMATION SYSTEMS AN INTRODUCTORY TEXTBOOK CHAPTER 7 Contents GIS and maps The visualization process Visualization and strategies The cartographic toolbox data characteristics, representation of these characteristics Examples, how to map: qualitative data, quantitative data, (terrain or statistical) elevation, time Map cosmetics: the finishing touch Map dissemination 1
GIS and maps In a GIS environment, maps can be used to: Input data (scanning/ digitizing existing maps) Query maps (to find available data, attribute values) Support visual (in stead of computational)analysis Display results of GIS operations Maps are not only final products (output)! Main characteristics of maps 1. Maps provide answers (in graphical form) to questions related to the 3 basic components of geographic data: geographic location thematic attributes time 2
Where do the ITC students come from? What is the type of land use? 3
When did the longest coastline occur? Where? Refers to geographic location (geometry) What? Refers to thematic attributes When? Refers to time More complex, combined questions are also possible Maps are efficient and effective means to transfer geo-spatial information to users! 4
Main characteristics of maps 2. Maps offer abstract representations (models) of reality, that are: simplified classified symbolised Representations of reality realistic more abstract 5
Main characteristics of maps 3. Maps are representations at scale Scale: ratio between distance on the map and corresponding distance in reality Scale distance distance on map in reality 1 : 5 000 1 cm 50 m 1 : 100 000 1 cm 1 km large small Scale indications verbal e.g. one-inch-to-the-mile representative fraction e.g. 1 : 100 000 graphical (scale bar) suitable in digital environments! e.g. 0 50 m 6
A map is: a representation or abstraction of geographic reality; a tool for representing geographic information in a way that is visual, digital or tactile. a reduced and simplified representation of (parts of) the Earth s surface on a plane. There are many types of maps Topographic map 7
Thematic maps population density watershed areas Tradition distinction in maps topographic maps accurate representation of the Earth s topography thematic maps one or more particular themes are emphasized Less relevant distinction in a digital environment 8
Dimensions in a map flat + height + time The visualization process Maps are the result of a visualization process 9
Visualization methods and techniques are applied using cartographic tools : functions (e.g. algorithms) rules (e.g. cartographic grammar, generalisation) habits or conventions (e.g. water in represented in blue) Visualization and strategies Visualization has several meanings: generic: to make info visible (presentation in graphical form) more specific: to use sophisticated computer technology and toolboxes to make data/ info visible for specific use: visual exploration this process is often called: scientific visualization: meant to stimulate thinking keywords: interaction, dynamics 10
Two main strategies: exploration, presentation private If maps are visually explored, we also talk about geovisualization Geovisualization is accelerated by: the possibility to generate maps at any stage in geoinformation processing hard- and software developments new output media changing needs / expectations of users availability of abundant data, from different sources 11
d information loss or gain Communication: particularly relevant for presentation The cartographic toolbox 1. Analysis of the characteristics of data What is the common denominator? Used for the title of the map (theme, area, year) What is the nature of the data or: what are the measurement scales? 12
Important Measurement scales are linked to the way in which people perceive visual variables (see further) The cartographic toolbox Basic elements of a map: point symbols line symbols area symbols text These elements can all be varied in appearance 13
Important Basic variations: Bertin s visual variables form/ shape orientation colour (=hue) grain/ texture lightness/ value size Bertin s visual variables 14
The visual variables enable observers to perceive: what belongs together, or is of equal importance order quantities an instant overview of the whole representation Important nominal ordinal interval ratio dimensions of the plane X X X X size (grey) value grain/ texture colour (hue) orientation shape X X X X X X X X X X 15
How to map? 1. Qualitative data, e.g. watersheds colour Qualitative data: watersheds value colour + brightness 16
2. Absolute quantitative data, e.g. number of inhabitants size Absolute quantitative data: no. of inhabitants value colour 17
3. Relative quantitative data, e.g. population density value Relative quantitative data: population density value (sequence!) colour + lightness 18
4. Elevation: terrain (relief) contours layer tints shading 3D view St. Pietersberg, the Netherlands 19
5. Elevation: statistical surface, e.g. number of inhabitants 6. Time (change over time) Single static map Multiple static maps Animated map 20
Example of mapping time: Urban growth of Enschede Growth of Enschede 800-1998, (view-only animation) 21
Map cosmetics: the finishing touch 1.Additional information marginal info (or metadata): makes the map more usable 2.Adding text improves the identification of features 22
Contrast improves overall map legibility Map dissemination (output) Map design is influenced by: data characteristics & user strategies (see before) output medium, e.g.: paper or screen maps Screen maps: often smaller legend is not always visible and they enable: access to a data base links to other data embedding in multi media dynamics and interaction 23
The Web as output medium increases the functions of maps: next to: insight in spatial data (traditional role) interface to additional information / services previews of data that can be acquired Classification of maps on the Web http://kartoweb.itc.nl/webcartography/webmaps/classification.htm http://kartoweb.itc.nl/webcartography/webbook/index1.htm 24