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- 1. Chapter 1 A gentle introduction to GIS
- 2. The nature of GIS ● The acronym GIS stands for geographic information system. ● Example usage of GIS – A geological engineer might want to identify the best localities for construct- ing buildings in an earthquake-prone area by looking at rock formation characteristics; – A mining engineer could be interested in determining which prospective copper mines should be selected for future exploration, taking into account parameters such as extent, depth and quality of the ore body, amongst others; – A forest manager might want to optimize timber production using data on soil and current tree stand distributions, in the presence of a number of operational constraints, such as the need to preserve species diversity in the area;
- 3. Spacial Data ● In the examples presented above, all the professionals work with positional data– also called spatial data. Spatial data refers to where things are, or perhaps, where they were or will be. To be more precise, these professionals deal with questions related to geographic space,which we define as having positional data relative to the Earth’s surface.
- 4. Dynamics and change ● Our world is dynamic, and our environment are constantly changing. ● Earth’s geography can have natural or man- made causes, or a mix of both. If it is a mix of causes, we usually do not fully understand the changes. ● In order to understand what is going on in our world, we study the processes or phenomena that bring about geographic change, so that we can take the best course of action.
- 5. El Nono, La Nina
- 6. Spatial and temporal dimensions ● The fundamental problem that we face in many uses of GIS is that of understanding phenomena that have a spatial or geographic dimension, as well as a temporal dimension. We are facing ‘spatio-temporal’ problems. This means that our object of study has different characteristics for different locations (the geographic dimension) and also that these characteristics change over time (the temporal dimension).
- 7. Defining GIS
- 8. Data capture and preparation ● In the El Nino case, data capture refers to the collection of sea water temperatures and wind speed measurements. This is achieved by placing buoys with measuring equipment at various places in the ocean. Each buoy measures a number of things: wind speed and direction; air temperature and humidity; and sea water temperature at the surface and at various depths down to 500 metres. For the sake of our example we will focus on sea surface temperature (SST) and wind speed (WS).
- 9. Data management ● data management refers to the storage and maintenance of the data transmitted by the buoys via satellite communication. This phase requires a decision to be made on how best to represent our data, both in terms of their spatial properties and the various attribute values which we need to store.
- 10. Data manipulation and analysis ● Data is georeferenced if it is associated with some position on the Earth’s surface, by using a spatial reference system. This can be achieved using (longitude, latitude) coordinates, or by other means. ● Spatial interpolation: The buoys only provide a set of sample observations of sea surface temperature.We can use these sample measurements to estimate the value of SST in places where we have not measured it, using a technique called spatial interpolation.
- 11. Data presentation ● The data presentation phase deals with putting it all together into a format that communicates the result of data analysis in the best possible way. ● Many issues arise in this phase. Among other things, we need to consider what the message is that we want to portray, who the audience is, what kind of presentation medium will be used, which rules of aesthetics apply, and what techniques are available for representation.
- 12. GISystems ● In the ‘wider’ sense: a functioning GIS requires both hardware and software, and also people such as the database creators or administrators, analysts who work with the software, and the users of the end product. ● In the ‘narrow’ sense: a computerized system that facilitates the phases of data entry, data management, data analysis and data presentation specifically for dealing with georeferenced data
- 13. GIScience ● The discipline that deals with all aspects of the handling of spatial data and geoinformation is called geographic information science (often abbreviated to geoinformation science or just GIScience). ● Is the scientific field that attempts to integrate different disciplines studying the methods and techniques of handling spatial information.
- 14. GIS applications ● aware of the difference between a geographic information system and and a GIS application. ● GIS software can (generically) be applied to many different applications. ● GIS applications usually have a clear-cut purpose, and these applications can be short- lived.
- 15. Spatial data and geoinformation ● data: we mean representations that can be operated upon by a computer. ● spatial data we mean data that contains positional values, such as (x, y) co-ordinates. ● geospatial data: spatial data that is georeferenced. ● information, we mean data that has been interpreted by a human being. Humans work with and act upon information, not data. ● Geoinformation is a specific type of information resulting from the interpretation of spatial data.
- 16. Data quality considerations ● information is intended to reduce uncertainty in decision-making, any errors and uncertainties in spatial information products may have practical, financial and even legal implications. ● If data is to be shared among different users, these users need to know not only what data exists, where and in what format it is held, but also whether the data meets their particular quality requirements. This ‘data about data’ is known as metadata.
- 17. Error in spatial data ● mistakes or variation in the measurement of position and/or elevation, in the quantitative measurement of attributes or in the labelling or classification of features. ● Gross errors : which must be detected and removed before the data is used, variations in the data caused by unavoidable measurement and classification errors. ● processing errors resulting from spatial analysis and modelling operations carried out by the system on the base data.
- 18. Data quality parameters ● Key components of spatial data quality include positional accuracy (both horizontal and vertical), temporal accuracy (that the data is up to date), attribute accuracy(e.g. in labelling of features or of classifications), lineage (history of the data including sources), completeness (if the data set represents all related features of reality), and logical consistency (that the data is logically structured).
- 19. The real world and representations of it ● One of the main uses of GIS is as a tool to help us make decisions. to help make these decisions, we need to represent some part of the real world as it is, as it was, or perhaps as we think it will be.
- 20. Models and modelling ● A representation of some part of the real world can be considered a model because the representation will have certain characteristics in common with the real world. ● A map is a miniature representation of some part of the real world. ● Databases are another important class of models. A database can store a considerable amount of data, and also provides various functions to operate on the stored data.
- 21. Static and dynamic models ● application models to refer to models with a specific application, including real-world models and so-called analytical models. ● ‘data modelling’ is the common name for the design effort of structuring a database. ● maps and databases can be considered static models. ● Dynamic models or process models, They emphasize changes that have taken place, are taking place or may take place sometime in the future. ● Simulation models are an important class of dynamic models
- 22. Maps ● the best known (conventional) models of the real world. ● A map is always a graphic representation at a certain level of detail, which is determined by the scale. ● Cartography, as the science and art of map making, functions as an interpreter, translating real world phenomena (primary data) into correct, clear and understandable representations for our use.
- 23. Databases ● A database is a repository for storing large amounts of data. It comes with a number of useful functions: – concurrent use – storage optimization, – Data integrity, – query facility – query optimization.
- 24. Spatial databases and spatial analysis ● In more recent years, spatial databases (also known as geodatabases) have emerged. Besides traditional administrative data, they can store representations of real world geographic phenomena for use in a GIS. These databases are special because they use additional techniques different from tables to store these spatial representations. ● A geodatabase is not the same thing as a GIS, though both systems share a number of characteristics.
- 25. Spatial analysis ● Spatial analysis is the generic term for all manipulations of spatial data carried out to improve one’s understanding of the geographic phenomena that the data represents.