Vector data model

Vector data model - geographical information system

1. Vector data model

2. CONTENTS INTRODUCTION SPATIAL DATA MODELS DATA REPRESENTATION VECTOR DATA MODEL TYPES OF VECTOR DATA MODELS ADVANTAGES AND DISADVANTAGES CONCLUSION REFERENCE

3. INTRODUTION A Geographic Information System (GIS) is a system designed to capture, store, manipulate, analyze, manage, and present all types of geographical data. GIS involves HW/SW, databases and models, people and processing for decision-making. The process is second stage in designing and implementing a data model. At present there are two main approaches in which computer can handle and display spatial entities. They are the raster and vector approaches.

4. SPATIAL DATA MODELS The traditionally spatial data are stored in the form of digital databases and presented them in the form of maps. Two basic types of spatial data models have been evolved for storing geographic data digitally. These are referred to as Raster Vector

5. DATA REPRESENTATION GIS data represent real object which can be stored under broad type known as raster data and vector data. Raster data is made up of a matrix of pixels (cells). The vector data is made up of points, polygons and lines. As compared to the vector data structure, the raster data structure is not particularly accurate as representing discrete features that is, those feature that have a distinct boundary and shape.

6. VECTOR DATA MODELS The vector data models use points, their XY co-ordinates to construct spatial features. The vector data models represent geographic features similar to the ways as maps do. Points represent geographic features too small to be depicted as lines or areas ; lines represents geographic features too narrow to depict as areas; and areas represents homogeneous geographic features.

7. TYPE OF VECTOR MODELS SPAGHETTI MODEL This is the simplest vector model with one to one translation of the graphical image on the map as the name suggests these vector files are simple lines with arbitrary starting and ending points just like following the path of the single stand of spaghetti through a pile of spaghetti on one's plate.

8. PROPERTIES OF SPAGHETTI DATA MODEL Point is enclosed as single XY co-ordinate pair. Line is encoded as a string of XY co-ordinate pairs. Polygon is encoded as a closed loop of XY co-ordinates that define its boundary. The Spaghetti model is a file of spatial data constructed in this manner is essentially a collection of co-ordinate strings with no inherent structure -hence the term spaghetti model. Although all the spatial features are recorded the spatial relationships between these features are not encoded.

9. TIN DATA MODEL The TIN model creates a network of triangles by storing the topological relationships of the triangles. The fundamental building block of the TIN data is the node. Nodes are connected to their nearest neighbors by edges, according to a set of rules. Left-right topology is associated with the edges to identify adjacent triangles. The TIN creates triangles from a set of points called mass points, which always become nodes. The user is not responsible for selecting; all the nodes are added according to a set of rules.

10. TIN DATA MODEL

11. DIFFERENCE BETWEEN VECTOR AND RASTER DATA MODEL Vector Data Model : [data models] A representation of the world using points, lines, and polygons. Vector models are useful for storing data that has discrete boundaries, such as country borders, land parcels, and streets. Raster Data Model : [data models] A representation of the world as a surface divided into a regular grid of cells. Raster models are useful for storing data that varies continuously, as in an aerial photograph, a satellite image, a surface of chemical concentrations, or an elevation surface. Both vector and raster data constitute of "latitudes and longitudes", only. The difference is in the way they are displayed. Latitudes and Longitudes in Vector data are displayed in the form of lines, points, etc. Latitudes and Longitudes in Raster data are displayed in the form of closed shapes where each pixel has a particular latitude and longitude associated with it.

12. ADVANTAGES OF VECTOR DATA Data can be represented its original resolution and form without generalization. Graphic output is usually more aesthetically pleasing (traditional cartographic representation). Since most data, e.g. hard copy maps, is in vector form no data conversion is required . Accurate geographic location of data is maintained.

13. DISADVANTAGES OF VECTOR DATA The location of each vertex needs to be stored explicitly. Algorithms for manipulative and analysis functions are complex and may be processing intensive. Often, this inherently limits the functionality for large data sets, e.g. a large number of features. Continuous data, such as elevation data, is not effectively represented in vector form. Usually substantial data generalization or interpolation is required for these data layers. Spatial analysis and filtering within polygons is impossible

14. Vector formats are either page definition languages or preserve ground co-ordinates. Common vector formats are Hardware Specific Formats/ Plotter formats PostScript Digital Exchange Format (DXF) Digital Line Graph (DLG) Shapefile SVG(Scalable Vector Graphics) Arc-Info Coverage Arc-Info Interchange (e00) GeoDatabase

15. CONCLUSION A data model in Geographic Information Systems is a mathematical construct for representing geographic objects . Integrated raster and vector processing capabilities are most desirable and provide the greatest flexibility for data manipulation and interpretation analysis. In many respects, vector and raster data models complement each other and get switched between along the processes of data collection, observation, analyses, and presentation.

16. REFERENCS Fundamentals of GIS(2007) by:Debashis Chakra borty-Rabi N.Sahoo-pp70-90. Remote sensing and G.I.S & Fundamentals of G.I.S (2000), M.Anji Reddy-pp:142-143. Introduction to G.I.S by: Kang- Tsung Chang –PP:31-53,117-133 G.I.S Basics (2008) by: Shahab fazal pp:155-203 www.wikipedia.com https://www.highpointnc.gov/gis/raster_v_vector_data.cfm