![]() ![]() In regional entities, those with name attributes and classification attributes are usually represented by polygons, such as administrative areas, land types, vegetation distribution, etc., those with scalar attributes are sometimes described by contours (such as topography, rainfall, etc.). Polygon data is the most important type of data to describe geographic information. It is an efficient spatial data structure. Compared with raster structure, data has high accuracy and occupies less space. Vector structure allows the most complex data to be stored with minimal data redundancy. Tracking digitizer generates vector structure digital map for map digitization, which is suitable for vector plotter drawing. A closed area is called a polygon because the boundary line of the area, like the line entity introduced earlier, can be regarded as a series of multiple and short line segments, each small line segment as a side of the area, so this area can be regarded as a polygon composed of these edges. ![]() Its boundary divides the whole space into two parts: the part containing the infinite point is called the exterior, and the other part is called the interior of the polygon. Polygon is a spatial area with arbitrary shape and completely closed boundary in the geographic information system. The coordinates are considered to be connected by line segments, which can vividly represent the linear objects of various shapes within a certain precision range. These small line segment sequences represent that only the coordinates of the endpoints of these segments are recorded in the vector structure, and the curves are represented as a coordinate sequence. When the curve is divided into many and short line segments, these small line segments can be approximated as straight line segments, and the curve can also be accurately divided by a series of lines. A curve is represented by a series of sufficiently short straight lines joined at the beginning and ending. ![]() For line entities, the digitizination is the quantization. In this case, the accuracy is much higher than that of the grid structure.įor point entities, only their coordinates and attribute codes are recorded in the vector structure. In fact, its accuracy is only limited by the accuracy of digital equipment and the length of digital records. The coordinate space is set as continuous, allowing precise definitions of arbitrary positions, lengths and areas. Much of the time, you will know or be told which projection to use based on your specific data/project.Another common graphic data structure in Geographic Information System is vector structure, that is to say, geographic entities such as points, lines and polygons are represented as accurately as possible by recording coordinates. For example Statistics Canada uses the Lambert projection for Canada (“ EPSG:3347”). Most common is UTM which splits the Earth into different linear regions, the code for the region encompassing British Columbia is “ EPSG:32610”īut many countries/regions use other specific projections which minimize distortion of that specific area. In linear units (e.g., meters) and are good for measuring distances. In angular units (degrees of latitude and longitude) and are good for locating places on Earth, for making global maps, and minimizing shape distortion. At a basic level, all you need to know is that some projections are: No projection is perfect (it’s impossible to perfectly flatten a 3d sphere) and each comprises on minimzing the distortion of shapes, distances, and areas of the Earth. There are many different projections and they are typically identified by an EPSG code. Generally speaking a coordinate reference system is how we project the 3D surface of the Earth onto a 2D shape for easy viewing Northwest Territories / Territoires du Nord-Ouest Prince Edward Island / Île-du-Prince-Édouard Newfoundland and Labrador / Terre-Neuve-et-Lab.
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