Chapter_3_Vector_Data_Model.pdf

Chapter 3 Vector Data Model Dr. Tareefa Alsumaiti & Abdallah Al Bizreh Feb 13 , 2024 Outline Methods of representing geographic space Representing Data with Vector Model Topology Exceptions in Topology Geodatabase Methods of representing geographic spac...

Chapter 3 Vector Data Model Dr. Tareefa Alsumaiti & Abdallah Al Bizreh Feb 13 , 2024 Outline Methods of representing geographic space Representing Data with Vector Model Topology Exceptions in Topology Geodatabase Methods of representing geographic space Vector Raster Concept of Vector and Raster Real World Raster Representation Vector Representation 0 1 2 3 4 5 6 7 8 9 0 R T 1 R T point 2 H R 3 R line 4 R R 5 R 6 R T T H 7 R T T polygon 8 R 9 R  Representing Data with Vector Models Vector Model: The vector data model uses the geometric objects of point, line, and polygon to represent spatial features. Points (nodes ): trees, wells, fire plugs, airports, cities.. etc. depends on scale 0 dimension/ has a location (X,Y). lines (arcs ): streams, streets, roads, river, valley..etc. 1 dimension/ has a length and location / 2 end points. A line may have additional points in between to mark the shape of the line. The shape of a line may be a connection of straight-line segments, or a smooth curve generated using a mathematical function. A line feature is made of a line or a set of lines.  Polygons ( areas ) : land parcels, cities, countries, land use, land cover (vegetated areas, urban areas, water bodies.).. etc. depends on scale 2 dimensions/ has an area, perimeter in addition to location. Made of connected, closed, nonintersecting lines, the perimeter or the boundary defines the area of a polygon. A polygon may also have a hole within its extent, resulting in an exterior and an interior boundary. A polygon can be stand alone or share boundaries with other polygons. A polygon feature consists of a polygon or a set of polygons.  The representation of simple features using points, lines and polygons, depends on map scale. For example, a city on a 1:1,000,000 scale map appears as a point. But the same city may appear as a polygon on a 1: 24,000 scale map. Because representation depends on shape, ArcGIS refers to files containing vector data as shapefiles. A more common name for shapefiles is “Feature” In vector data many attributes could be saved with each vector element (name, abbreviation, population, speed, width, ….etc)  Topology (it's all about relationship) Topology basically refers the relationship between things, and in the realm of GIS, Topology refers to the relationship between spatial features or objects. Topology is all about relationship and special programming applied to GIS data so that the features have “intelligent” connections with other features. There are rules that applies to the feature itself, and other rules that applies to relationship between different features With topology each feature has the following characteristics: Knows where it is: a feature position is part of the data knowledge. Knows what is around: the connected and surrounding features are recognized. Has recognized spatial relationships with other features. Has length, distance, perimeter, and area information. Knows how to get around, get from one location to another using connections and paths.  Examples on Topology The following are some real-world applications of topology rules: – Counties/districts must not overlap. – County/district must not have gaps. – City boundaries and districts must cover each other. – Contour lines must not intersect. – Roads must be connected – Label points must be properly inside polygons. Incorrect Topology Correct Topology Example on Topology Rules in Polygons Example on Topology Rules in Lines Example on Topology Rules in Points  Exceptions in Topology Sometimes exceptions can be added depending on the real world: example: dead- end roads , parking lot..etc. To apply topology rules on features a topology package is needed  Geodatabase The geodatabase is part of ArcObjects, a collection of thousands of objects, properties, and methods that provides the foundation for ArcGIS. The geodatabase organizes vector data sets into feature classes and feature datasets A feature class stores spatial data of the same geometry type. A feature dataset stores feature classes that share the same coordinate system and area extent. In a geodatabase, feature classes can be standalone feature classes or members of a feature dataset.  These two classes will have the same coordinate system of the “Feature Dataset” Standalone feature class  Examples of Geodatabases UAE_Roads is a dataset used for Network Analysis, with UAE_Roads_ND is the definition of this network analysis dataset (To do network analysis I must use GeoDatabase) Roads Datasert has a topology defined in Roads_Topology (to apply topology rules I must use GeoDatabase)  Advantages of the Geodatabase The hierarchical structure of a geodatabase is useful for data organization and management. The geodatabase, which is part of ArcObjects, can take advantage of object-oriented technology. The geodatabase offers on-the-fly topology, applicable to features within a feature class or between two or more participating feature classes. Thousands of objects, properties, and methods in ArcObjects are available for GIS users to develop customized applications. ArcObjects provides a template for custom objects to be developed for different industries and applications. The integration of spatial and attribute data in the geodatabase facilitates spatial query task.  Questions? References Kang-Tsung Chang, Introduction to Geographic Information Systems. Chapter 3. 9th Ed. New York: McGraw Hill.