GIS Spatial data types (Raster , Vector data)

Introduction

GIS information can be isolated into two classifications: spatially referenced information which is spoken to by vector and raster form (including imagery) and property of data is stored in tabular forms characterized as attribute data. Inside the spatial referenced information gathering, the GIS information can be additionally grouped into two distinct types: vector and raster.  Lets dive deeply in vector and raster data.

Vector Data:

Vector data is based on geometrical shapes used for showing features in GIS environments. Vector data split into three types: polygon, line (or arc) and point data. Polygons are used to represent areas such as the boundary of a city (on a large scale map), lake, or forest.  Lines are used to represent linear features such as roads, street, river etc. Points are used to represent specific features locations such as towers, water tanks, poles, office locations etc

 Basic Elements:

• Location (x,y) or (x,y,z)

• Explicit, i.e. pegged to a coordinate system

• Different coordinate system (and precision) require different values

·         e.g. UTM as integer (but large)

·         Lat, long as two floating point numbers +/-

• Points are used to build more complex features

VECTOR FORMATS

1. Shapefile

Contains:

GIS DATA MODEL

• o Point, or multi-point
• o Line, or polyline
• o Polygon

2. Coverage

Contains:

• o Point, or node
• o Arc, or line
• o Polygon
• o Label

 EXAMPLES

1. • Administrative borders
2. • Linear features
3. • Roads
4. • Rivers
5. • Discrete habitat boundaries

Raster data :

Raster data consists of a matrix of cells (or pixels) organized into rows and columns (or a grid) where each cell contains a value representing information, such as temperature. Rasters are digital aerial photographs, imagery from satellites, digital pictures, or even scanned maps. Raster data is used in a

GIS application when we want to display information that is continuous across an area and cannot easily be divided into vector features.

Basic Elements:

• Extent
• # Rows
• # Columns
• Origin
• Orientation
• Resolution: pixel = grain = grid cell

EXAMPLES

• • Temperature (air, water)
• • Air pressure
• • Ecotones
• • Soil ph
• • Precipitation
• • Salinity
• • Elevation & its derivatives
• • Flow
• • Direction, distance
• • Reflectance (photography/imagery)