Digital Cartography Data and GIS data Models (10).pdf

Digital Cartography Data and GIS data Models Continuous and Discrete Data Dis crete data "Vector" It is geographic data that only occurs in specific locations and can exist independently.​ Continuous data "R as ter" It has no clearly defined boundaries. Some continuous data examples are temperat...

Digital Cartography Data and GIS data Models Continuous and Discrete Data Dis crete data "Vector" It is geographic data that only occurs in specific locations and can exist independently.​ Continuous data "R as ter" It has no clearly defined boundaries. Some continuous data examples are temperature, rainfall, and elevation measurements. The spatial characteristics of features can be stored in GIS in one of 2 ways: Vector Raster Vector data is a data structure that can be used to store spatial data. It is used to represent real-world features and assign attributes to those features. It comprises of individual points, stored as coordinate pairs that indicate a physical location in the world. Data in this format can have a geometry type of point, line, and polygon. Point: They are simply X, Y, and Z coordinates. It typically represents a geographic feature too small to be displayed as a line or area. These features also consist of a node and vertex. They generally indicate distinct, discrete components such as buildings, trees, power poles, sample locations, etc. They only have the property of the location. Line: They are composed of many (at least 2) points that are connected. It represents linear features such as roads, streams, faults boundaries, flight paths, and contours. E.g., If you want to express a route on a map, you can use line vector data to display it on a map. Polygon: It consists of 3 or more vertices connected and closed. They have attributes that describe the geographic feature they represent. They are enclosed areas like dams, lakes, vegetation, country boundaries, etc. Like polyline features, they are created from vertices connected with a continuous line. However, because a polygon always describes an enclosed area, the first and the last vertices should always be in the same place. E.g., If you want the closed boundary of a rock on a map, then you can use polygon vector data to display it on a map. Raster data is made up of pixels (also referred to as grid cells). Each pixel is associated with a specific geographical location. Raster Representation • Rasterization: covert vector data to raster data. • Vectorization: convert raster data to vector data. Vector Data Formats Some of the essential file formats are: • Shapefile (SHP): It is a popular geospatial vector data format for a geographic information system (G.I.S .) software storing geographic features, location, shape, and attributes. • Keyhole Markup Language (KML.): It is a standard format for sharing geographic data and visualizing it in threedimensional earth browsers like Google Earth. KML Boundary • AutoCAD Drawing Exchange Format (DXF): A CAD data file format is often used to share drawing data between other CAD programs. Contour lines in DXF format to open it in AutoCAD • Comma Separated Values (CSV): It can be visualized as a table that can only represent point data. It is a delimited text file that uses a comma to separate values.​ XYZ values in CS V format • Geodatabase (GDB): An ArcGIS-specific format for editing and data management. • OpenStreetMap (OSM): It is a key value format written in XML for creating and sharing map information. Raster Data Formats • Portable Network Graphics (PNG): It is a raster file format that allows lossless Compression. Lossless compression reduces file size without decreasing image quality. They are designed for efficient viewing in webbased browsers such as Internet Explorer, Firefox, and Chrome. Land map in PNG format • JPEG (Joint Photographic Experts Group): It is a commonly used method of lossy compression for photographic images. In lossy compression, the data in a file is removed and not restored to its original form after decompression. This data loss is not usually noticeable to the naked eye. • Tag Image File Format (TIFF): A computer file that stores raster graphics and image information. They hold high-quality images and have either a .tiff or .tif extension. They are a lossless form of file compression. Orthomos aic map in TIFF format • GR ID: It is a raster GIS file format developed by Esri. It has a proprietary binary format and a non-proprietary ASCII format. The binary format is widely used within Esri software, such as ArcGIS . In contrast, the ASCII format is used as an exchange, or export format, due to the simple and portable ASCII file structure. • IMG: It is a proprietary, partially documented format for multi-layer geo-referenced raster images developed originally for use with ER DAS IMAGINE software. This format is used widely for processing remote sensing data since it provides a framework for integrating sensor data and imagery from many sources. • USGS Digital Elevation Model (DEM): It is a popular file format due to widespread availability, the simplicity of the model, and the extensive software support for the format. Each pixel value in these grid-based DEMs denotes spot elevations on the ground, usually in feet or meters. In their native format, they are written as ANSI-standard ASCII characters in fixed-block format. Digital Surface Model Vector : Advantages & Disadvantages Advantages Topology: It can be wholly described and easy to maintain. • Storage: Easier to store since it requires less disk storage. • Spatial res olution: It has high spatial resolution and high-precision graphics. • Accuracy: It can represent all features will high accuracy. • R epres entation: Sharp, Clean, scalable, and aesthetically pleasing. • Dis advantages • Complexity: It has a complex data structure and algorithms. • Time Cons uming: It depends on the size and number of features, so the editing and processing of vector data can be pretty time-consuming. • Continuous Data: Continuous data is poorly stored and displayed. such as elevation data, is not effectively represented in vector form. • Compatibility: It is not compatible with remote sensing data. Raster : Advantages & Disadvantages Advantages • Data structure: It has a simple matrix of cells with values representing a coordinate. • Simulation: It is easy because cells have the same size and shape. • Performance: It has a good ability to represent continuous features and perform surface analysis. • Compatibility: Compatible with remote sensing images and aerial images. • It does not require a lot of time to obtain it Disadvantages • Representation: It is hard to represent objects less than cell size. • Spatial Resolution: Finer resolution generates vast amounts of data. • Size: Greater storage needed • Topology: It is challenging to represent topological connections. • Accuracy: Precise locations may not be recorded as accurately as Vector data. Difference between Raster Data and Vector Data Raster Data Vector Data Made up of pixels Made of a series of X,Y coordinates Continuous data Discrete Data Greater storage needed Little storage space Data structure is simple Data structure is complex Depend on pixel size for resolution Doesn’t depend on pixel size for resolution Represents data in cells or grid Represents data using vertics Larger file size Smaller file size E.g.,Elevation Map , Slope Map E.g., Points , Lines , Polygons Thank You!