ESRI Shapefile – what is this whole shape-thing? ESRI Shapefile – a popular vector data format for GIS programs which stores location data in graphic forms. Each such location has a set of attributes that describes it and provides information on a given object, such as their geographical position. Shapefile operates on points, lines, and polygons – each representing a given object type on the map:
Shapefile consist of a couple to a dozen or so files. Three of them are necessary to use Shapefile:
These form the spine of a Shapefile. If one of them is missing, we will not able to use our data in any GIS program, such as QGIS or ArcGIS. There is also the .pri file which provides geographical reference and indicates the coordinate system that our Shapefile was stored in; it does not influence whether the file can be read, though. Where you’re at? – on coordinate systems The Earth is a geoid so it is tricky to present it on a map. This is why coordinate systems were invented which can transfer the Earth’s surface directly onto a map, minimizing the distortions caused by transferring a sphere (our planet) onto a plane (the map). Coordinate system – a mathematical equation which converts geographical coordinates into map coordinates, so that any given points on the Earth maintain their proportions. There are hundreds of coordinate systems and each corresponds to a particular area on Earth. Some systems are used to create maps in a given scale, and there are even official coordinate systems for countries and geographical regions. Coordinate systems in Poland Poland has two official coordinate systems: 1992 and 2000. Each is used to create different types of maps. The 1992 system is an official coordinate system used in the whole Poland. It is used for all the maps with a scale smaller than 1:10,000 (i.e. with the scale denominator larger than 10,000, e.g. 1:20,000, 1:50,000 etc.). The EPSG code (more on that later) for this system is 2180. The 2000 system is also a coordinate system used in Poland, however, it is used for maps with a scale larger than 1:10,00 (i.e. with the scale denominator smaller than 10,000, such as 1:5000, 1:2000 etc.). The 2000 system divides Poland into four zones along the meridians: 15E, 18E, 21E, 24E. Each zone is marked with a number between 5 and 8. Depending on the location of a given point on a map, we should use the corresponding coordinate system. The EPSG code for each zone is: Zone V – EPSG code 2176 Zone VI – EPSG code 2177 Zone VII – EPSG code 2178 Zone VIII – EPSG code 2179 What is the EPSG code? The ESPG code is a universal identification code dedicated to coordinate systems. The same coordinate system may appear under various names in various sources but it will always have the same ESPG code. Knowing the ESPG code will prevent you from making any mistakes while working with maps, and especially with coordinate systems. Create a map in QGIS! QGIS is an open-source GIS program. It processes spatial data, such as Shapefiles and raster files, lets you create maps and analyzes said data. It is free and accessible to anyone. You can download it from this website: www.qgis.org. I strongly recommend to try it out! I am aware that some of the above might seem trivial to you but these are the basic terms you should know, if you plan to work with the GIS technology. If you have any questions, do not hesitate to contact me at [email protected] Check out the tMap app on your phone.
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