GIS A Geographic Information System GIS can be

GIS • A Geographic Information System (GIS) can be defined as a set of hardware, software, data, methods and people. • Its aim consists in the management, display and analysis of geographically referenced information. • Each entity of land has spatial information! • GIS allows us to visualize, understand discover the spatial relationships between geodata in form of maps, charts, reports, etc.

GIS

GIS What can we do with GIS? We can map: • the position of things (coordinates) • the quantities of things (population) • the densities of things (density of population) • what happens inside a specific area • what is nearby within a specific distance • the evolution/change of phenomena • …and much more!

GIS Spatial data links alphanumeric information with a specific location. Alphanumeric information is displayed in a computer screen in reference to the location of objects of the real world. A data model in GIS is a mathematical construct for representing geographic objects or surfaces as data. • The vector data model represents geography as collections of points, lines, and polygons • The raster data model represents geography as cell matrices that store numeric values

GIS Spatial information is displayed in a GIS using layers of spatial information. A layer could be based on a raster or vector data model. The Raster data model is used mainly to represent continues features such as elevation, temperature or aerial and satellite images. The Vector data model is generally used in order to represent discrete features (e. g. trees, roads, administrative boundaries, etc. ).

GIS Vector Point Raster Polyline Polygon

GIS The vector data model

GIS 2 1 3 Which is the most expensive? Point 1 452896, 4785263 Point 2 456982, 4589621 Point 3 562841, 4785699 ID Name Owner Price 1 ABC Joe 50 2 JKL Bill 63 3 QWY Mary 85

GIS 2 1 3 Point 1 452896, 4785263 Point 2 456982, 4589621 Point 3 562841, 4785699 ID Name Owner Price 1 ABC Joe 50 2 JKL Bill 63 3 QWY Mary 85

GIS Polyline Vertex Node

GIS Polygon-polyline topology A polygon consists of lines, which consist of points, which consist of coordinates

GIS Topological errors

GIS Shapefile The shapefile format is a popular geospatial vector data format for geographic information system (GIS) software. It is a proprietary format of ESRI. Mandatory files • . shp — shape format; the feature geometry itself • . dbf — attribute format; columnar attributes for each shape, in d. Base IV format • . shx — shape index format; a positional index of the feature geometry to allow seeking forwards and backwards quickly Other files • . prj — projection format; the coordinate system and projection information, a plain text file describing the projection using well-known text format • . sbn and. sbx — a spatial index of the features • . shp. xml — geospatial metadata in XML format, such as ISO 19115 or other XML schema

GIS Other vector formats • DXF – Proprietary of Auto. CAD, originally intended for technical drawings • GML – Geographical Markup Language, an open standard • KML – Keyhole Markup Language, also an open standard, made popular by Google. Earth • “coverage” – Legacy format, proprietary, from ESRI, dating back to the ’ 80 s

GIS Spatial databases • Geodatabase – Proprietary of ESRI • Personal geodatabase • File geodatabase • Relational database • Post. GIS – a spatial database extender for Postgre. SQL objectrelational database • Spatia. Lite – A spatial extension to SQLite, a single-file portable relational database

GIS Raster data • Raster data better describe continuous variables and phenomena • Satellite images, aerial photos, DEMs, etc. • Well suited for spatial analysis • Not well suited for cartography

GIS The raster data model

GIS Raster layers can store different data types (the values inside the cells) • Integer –byte (0 -255, one cell = 1 byte) • example: most satellite images –x 2, signed or unsigned (one cell = 2 bytes) • example: DEMs –x 4, larger figures (one cell = 4 bytes) –can have attribute tables • Real (floating) –x 4 (one cell = 4 bytes) • example: vegetation indexes –x 8, higher accuracy, seldom used (one cell = 8 bytes) The file size increases correspondingly, as well as the processing time

GIS It is easy to convert most vector data to raster It is very hard (almost impossible) to convert decently raster data to vector

GIS raster file formats • TIFF – – more than a format, is a container can accomodate multiple band, compressed or not compression is usually lossless Geo. Tiff include also georeferencing information • JPEG – created for storing picture using a highly efficient lossy compression – JPEG 2000 can include georeferencing information and lossless compression • GRID – proprietary of ESRI • Mr. SID – patented, created for GIS, optimized for image viewing – compressed, lossless, not so common • Many other free or proprietary formats – QGIS relies upon the GDAL library for data reading/writing; for a full listing of formats that can be used by GDAL, see: http: //www. gdal. org/formats_list. html

GIS Where to find downloadable data • A categorized list of links to over 300 sites providing freely available geographic datasets - all ready for loading into a Geographic Information System – http: //freegisdata. rtwilson. com • The Map Library is a source of public domain basic map data concerning administrative boundaries in Africa. The data is broken down into manageable chunks to make it easier to download for those with poor internet connections – http: //www. mapmakerdata. co. uk. s 3 -website-eu-west 1. amazonaws. com/library/index. htm • The Open Source Geospatial Foundation (OSGeo), a good starting point – http: //www. osgeo. org/geodata • . . . and of course Wikipedia – http: //en. wikipedia. org/wiki/List_of_GIS_data_sources

GIS • Metadata is "data about data". Example: the card catalogue of a library. Metadata provide information about one or more aspects of the data, such as: • – – – • • means of creation of the data purpose of the data time and date of creation creator or author of the data physical location, e. g. on a computer network standards used Metadata is data. As such, metadata can be stored and managed in a database, often called a metadata registry or metadata repository. They apply to many different sectors: geospatial metadata is a type of metadata that is applicable to objects that have an explicit or implicit geographic extent

GIS Geospatial Metadata Standards: • ISO/TC 211 is a standard technical committee formed within ISO – task: covering the areas of digital geographic information and geomatics. It is responsible for preparation of a series of International Standards and Technical Specifications numbered in the range starting at 19101 • ISO 19115: Geographic information – Metadata – It defines how to describe geographical information and associated services, including contents, spatial-temporal purchases, data quality, access and rights to use. • ISO 19139 Geographic information Metadata XML schema implementation – provides a spatial metadata XML (sm. XML) encoding, an XML schema implementation derived from ISO 19115 – describe, validate, and exchange geospatial metadata

GIS

GIS • The Geo. Network opensource project is a free and open source cataloging application for spatially referenced resources. • It is used by large organizations to maintain and share a huge amount of information • Examples: – – – FAO http: //www. fao. org/geonetwork WFP http: //vam. wfp. org/geonetwork UNEP http: //www. ecomundus. net CGIAR http: //geonetwork. csi. cgiar. org WHO http: //www. who. int/geonetwork Many other national and international portals • Get a full list at http: //geonetwork-opensource. org/