地理信息系統(tǒng)gisppt課件-展示頁
2025-05-21 13:55本頁面
【正文】 lly displayed on a map through symbology and annotation. 2. 3 Map information Geographic Information System GIS ?Spatial Component Location Information Where is it? All of the data in a GIS are georeferenced. ?Attribute Component Descriptive Information (characteristics) What is it? Geographic Information System GIS Geographic Data: Spatial + Attribute ... Geographic Information System GIS Geographic Data: Geographic Information System GIS Introduction 1. What is GIS? 2. In the beginning.... there were maps 3. Raster and vector 4. GIS = software + data.... 5. The significance of scale 6. Basic functions of GIS Geographic Information System GIS Maps in bits Computers store information in sequences of binary digits (bits), which form a code for every possible number or letter. Geographic Information System GIS This fits with the way maps reference geographical locations on the earth’s surface, through a system of coordinates. All locations and shapes can be defined in terms of x and y coordinates from a given grid system: it is these numerical values which are used to translate map information into digital form. Geographic Information System GIS Vector data There are two fundamental methods of storing map information in digital form, raster and vector. In vector data the features are recorded one by one, with shape being defined by the numerical values of the pairs of xy coordinates. A point is defined by a single pair of coordinate values. A line is defined by a sequence of coordinate pairs defining the points through which the line is drawn. An area is defined in a similar way, only with the first and last points joined to make a plete enclosure. Geographic Information System GIS In vector data the position and shape of the building is captured as a series of four pairs of numerical coordinates. Geographic Information System GIS Raster data In raster data the entire area of the map is subdivided into a grid of tiny cells. A value is stored in each of these cells to represent the nature of whatever is present at the corresponding location on the ground. Raster data can be thought of as a matrix of values. Geographic Information System GIS ?The values recorded in the cells are either white, blue or red. ?To reproduce the image the puter reads each of these cell values one by one and applies them to the pixels on the screen. Geographical Information System GIS Vector v Raster Vector: Relatively low data volume Faster display Can also store attributes Less pleasing to the eye Raster: Relatively high data volume Slower display Has no attribute information More pleasing to the eye Geographical Information System GIS Geographical Information System GIS ?In this example the raster data looks nicer but, as you zoom in, the pixel structure bees obvious. Eventually the image looks like a piece of modern art rather than a detail of a map! ?The definition of the features is dependent upon the size of the individual grid cells – the resolution. ?The vector data is more like a graph with a line drawn between points, the width staying the same however close you zoom. Geographical Information System GIS Geographical Information System GIS Geographical Information System GIS Geographical Information System GIS Geographical Information System GIS Introduction 1. What is GIS? 2. In the beginning.... there were maps 3. Raster and vector 4. GIS = softwar
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