Vector data model

CONTENTS

• INTRODUCTION

• SPATIAL DATA MODELS

• DATA REPRESENTATION

• VECTOR DATA MODEL

• TYPES OF VECTOR DATA MODELS

• ADVANTAGES AND DISADVANTAGES

• CONCLUSION

• REFERENCE

INTRODUTION

• A Geographic Information System (GIS) is asystem designed to capture, store, manipulate,analyze, manage, and present all types ofgeographical data.

• GIS involves HW/SW, databases and models,people and processing for decision-making.

• The process is second stage in designing andimplementing a data model.

• At present there are two main approaches inwhich computer can handle and display spatialentities.

• They are the raster and vector approaches.

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 storinggeographic data digitally.

• These are referred to as

Raster Vector

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 notparticularly accurate as representing discrete features that is, those feature that

have a distinct boundary and shape.

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 theways as maps do.

Points represent geographic features too small to be depicted as linesor areas; lines represents geographic features too narrow to depict asareas; and areas represents homogeneous geographic features.

TYPE OF VECTOR MODELS• SPAGHETTI MODEL

This is the simplest vector model with one to one translation of thegraphical image on the map as the name suggests these vector files aresimple lines with arbitrary starting and ending points just likefollowing the path of the single stand of spaghetti through a pile ofspaghetti on one's plate.

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-ordinatesthat define its boundary.

• The Spaghetti model is a file of spatial data constructedin this manner is essentially a collection of co-ordinatestrings with no inherent structure-hence the termspaghetti model.

• Although all the spatial features are recorded the spatialrelationships between these features are not encoded.

TIN DATA MODEL

• The TIN model creates a network of triangles by storingthe 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 associatedwith the edges to identify adjacent triangles.

• The TIN creates triangles from a set of points called masspoints, which always become nodes. The user is notresponsible for selecting; all the nodes are added accordingto a set of rules.

TIN DATA MODEL

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.

ADVANTAGES OF VECTOR DATA• Data can be represented its original resolution and form without

generalization.

• Graphic output is usually more aesthetically pleasing (traditionalcartographic representation).

• Since most data, e.g. hard copy maps, is in vector form no dataconversion is required.

• Accurate geographic location of data is maintained.

DISADVANTAGES OF VECTOR DATA

The location of each vertex needs to be stored explicitly.

Algorithms for manipulative and analysis functions are complex andmay be processing intensive. Often, this inherently limits thefunctionality for large data sets, e.g. a large number of features.

Continuous data, such as elevation data, is not effectively representedin vector form. Usually substantial data generalization or interpolationis required for these data layers.

Spatial analysis and filtering within polygons is impossible

• 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

CONCLUSION

• A data model in Geographic Information Systems is a mathematicalconstruct for representing geographic objects .

• Integrated raster and vector processing capabilities are most desirableand provide the greatest flexibility for data manipulation andinterpretation analysis.

• In many respects, vector and raster data models complement eachother and get switched between along the processes of data collection,observation, analyses, and presentation.

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