WRM 362_Applied RS and GIS_Visualisation.pdf

Kwame Nkrumah University of Science & Technology, Kumasi, Ghana Lecture 3 Visualization and dissemination Ing. G. Ashiagbor Dept. Wildlif...

Kwame Nkrumah University of Science & Technology, Kumasi, Ghana Lecture 3 Visualization and dissemination Ing. G. Ashiagbor Dept. Wildlife and Range Management Faculty of Renewable Natural Resources E-mail: [email protected] Office # : 115 FRNR  GISs and maps There is a strong relationship between maps and GISs. Maps play a role at any moment one uses a GIS. They can be used as input, to verify data, to prepare a spatial analysis and of course to present results. As soon as a “where?” crops up in a question, a map can often be the most suitable tool for solving the question and providing the answer. As soon as the location of geographic objects is involved (“where?”), a map becomes useful. However, maps can do more than just provide information on location. They can also inform about the thematic attributes of the geographic objects to be found in them. www.knust.edu.gh  GISs and maps Maps can deal with questions/answers related to the basic components of spatial or geographic data: location (geometry), characteristics (thematic attributes) and time, and combinations thereof. As such, maps are the most efficient and effective means of transferring spatial information. The map user can locate geographic objects, while the shape and colour of signs and symbols representing the objects inform about their characteristics. They reveal spatial relations and patterns and offer the user insight into and overview of the distribution of particular phenomena. An additional characteristic of on-screen maps is that these are often interactive and have a link to a database; this allows for more complex queries. www.knust.edu.gh GISs and maps C. Board (1990) defines a map as “a representation or abstraction of geographic reality. A tool for presenting geographic information in a way that is visual, digital or tactile.” The first sentence in this definition contains three key words. The “geographic reality” represents the object of study: i.e. our world. “Representation” and “abstraction” refer to models of these geographic phenomena. The second sentence reflects the appearance of the map. Can we see or touch it? Or is it stored in a database? In other words, a map is a reduced and simplified representation of the Earth’s surface, or parts of it, on a plane. www.knust.edu.gh Topographic and thematic Maps A topographic map visualizes, limited by its scale, the Earth’s surface as accurately as possible. This may include infrastructure (e.g. railways and roads), land use (e.g. vegetation and built-up areas), relief, hydrology, geographic names and a reference grid. Thematic maps represent the distribution of particular themes. One can distinguish between socio-economic themes and physical themes. thematic maps also contain some information found in the topographic map, so as to provide a geographic reference to the theme represented www.knust.edu.gh  Thematic map Topo map www.knust.edu.gh Topographic and thematic Maps A topographic map visualizes, limited by its scale, the Earth’s surface as accurately as possible. This may include infrastructure (e.g. railways and roads), land use (e.g. vegetation and built-up areas), relief, hydrology, geographic names and a reference grid. Thematic maps represent the distribution of particular themes. One can distinguish between socio-economic themes and physical themes. thematic maps also contain some information found in the topographic map, so as to provide a geographic reference to the theme represented www.knust.edu.gh The visualization process the cartographic visualization process is considered to be the translation or conversion of spatial data from a database into graphics, which are predominantly map-like products. During the visualization process, cartographic methods and techniques are applied. These can be considered to form a kind of grammar that allows for the optimal design and production of the maps, depending on the application www.knust.edu.gh  The visualization process The visualization process can vary greatly depending on where in the spatial-data handling process it takes place and the purpose for which it is needed. Visualizations can be, and are, created during any phase of the spatial-data handling process as indicated before. the visualization process is guided by the question “How do I say what to whom?” – “How” refers to cartographic methods and techniques; – “I” represents the cartographer or map-maker; – “say” deals with communicating in graphics the semantics of the spatial data; – “What” refers to the spatial data and its characteristics, (for instance, whether they are of a qualitative or quantitative nature); – “Whom” refers to the map audience and the purpose of the map—a map for scientists requires a different approach than a map on the same topic aimed at children. www.knust.edu.gh The visualization process www.knust.edu.gh  The visualization process The visualization process is always influenced by several factors, i.e. the answers to questions: 1. What will be the scale of the map: large, small, other? This introduces the problem of generalization. Generalization addresses the meaningful reduction of the map content during scale reduction. 2. Are we dealing with topographic or thematic data? These two categories have traditionally resulted in different design approaches, as was explained in the previous subsection. 3. More important for the design is the question of whether the data to be represented are of a quantitative or qualitative nature The sentence “How do I say what to whom, and is it effective?” guides the cartographic visualization process and summarizes the cartographic communication principle. www.knust.edu.gh  The cartographic toolbox: What kind of data do I have? To find the proper symbology for a map one has to analyse the cartographic data. The core of this process of analysis is to access the characteristics of the data to find out how they can be visualized, so that the map user will interpret them properly. Data will be of a qualitative or quantitative nature. Qualitative data is also called nominal data, which exists as discrete, named values without a natural order amongst the values. www.knust.edu.gh  The cartographic toolbox: What kind of data do I have? Quantitative data can be measured, either along an interval or ratio scale. – For data measured on an interval scale, the exact distance between values is known, but there is no absolute zero on the scale. Temperature is an example: 40 C is not twice as hot as 20C, and 0C is not an absolute zero. – Quantitative data with a ratio scale do have a known absolute zero. An example is income: someone earning $100 earns twice as much as someone with an income of $50. In order to generate maps, quantitative data are often classified into categories according to some mathematical method. In between qualitative and quantitative data, one can distinguish ordinal data. These data are measured along a relative scale and are as such based on hierarchy. For instance, one knows that a particular value is “more” than another value, such as “warm” versus “cool”. www.knust.edu.gh The cartographic toolbox: What kind of data do I have? www.knust.edu.gh  The cartographic toolbox: How can I map my data? Basic elements of a map, irrespective of the medium on which it is displayed, are point symbols, line symbols, area symbols, and text. The appearance of point, line, and area symbols can vary depending on their nature. Points can vary in form or colour to represent the location of shops or they can vary in size to represent aggregated values (e.g. number of inhabitants) for an administrative area. Lines can vary in colour to distinguish between administrative boundaries and rivers, or vary in shape to show the difference between railroads and roads. Areas follow the same principles: differences in colour distinguishes between different vegetation. www.knust.edu.gh The cartographic toolbox: How can I map my data? Six visual variables www.knust.edu.gh  The cartographic toolbox: How can I map my data? Basic elements of a map, irrespective of the medium on which it is displayed, are point symbols, line symbols, area symbols, and text. The appearance of point, line, and area symbols can vary depending on their nature. Points can vary in form or colour to represent the location of shops or they can vary in size to represent aggregated values (e.g. number of inhabitants) for an administrative area. Lines can vary in colour to distinguish between administrative boundaries and rivers, or vary in shape to show the difference between railroads and roads. Areas follow the same principles: differences in colour distinguishes between different vegetation. www.knust.edu.gh  Kwame Nkrumah University of Science & Technology, Kumasi, Ghana THANK YOU