#Raster and vector data model in gis registration#
#Raster and vector data model in gis series#

Vector Data are in the form of point, line and polygon that are recorded in Spatial information as x and y coordination. Thus the vector attributes recorded against feature ID numbers are assigned by system itself.

#Raster and vector data model in gis series#

The line features as well as polygons features are recorded as a series of x and y coordinates. The point features are recorded as single x and y pair of coordinates. In the vector data, the spatial information are recorded as x, y coordinates. Vector models are useful for storing data that has discrete boundaries, such as country borders, land parcels, and streets. Vector Data: A representation of the world using points, lines, and polygons.

Projection transformations are time consuming and difficult.

Network linkages are difficult to establish.

The raster maps are considerably less beautiful than line maps.

The use of large cells to reduce data volumes means that phenomenologically recognizable structures can be lost and there can be a serious loss of information.

Overlay analysis is easy to perform with raster model.

Continuous features are best represented using raster.

Compatible with remotely sensed imagery.

The rows of the matrix are parallel to X – axis and the columns are parallel to the Y-axis. Pixel or cell are arranged in rows and columns that construct a certain matrix format. A pixel or cell represent a square kilometer, a square meter or even a square centimeter. The pixel can be any size, but they should be small enough to perform maximum detail analysis. This type of spatial data usually bulky and required large storage capacity.Įxample of raster data as satellite imagery, digital elevation model (DEM), aerial photography, Scanned maps etc.Īll pixels in a raster data must be the same size, determining the resolution. Each pixel preserves locational information. It is represented by matrix or grid of pixel. Raster data comes in the form of individual pixels. Thus the attribute is represented as a single value of each pixel or cell that is called as DN (Digital Number Value). When the data is geo-referenced the data give each and every pixel its locational information. a road can be represented as a line at a smaller scale or as a polygon at a larger scale.The raster data are the data that have individual pixels where each pixel has its spatial location in referenced to real earth. A real-world entity could be represented by different types of vector features depending on the map scale used in an application (e.g. In the above figure, the real world is represented by a series of lines (roads and highways) and one polygon (the river). Polygons are closed areas that can be made up of a circuit of line segments. Lines are spatial objects made up of connected points (nodes) that have no width. Points are spatial objects with no area but can have attached attributes since they are a single set of coordinates (X and Y) in a coordinate space. A vector representation is composed of three main elements: points, lines, and polygons. The concept assumes that space is continuous, rather than discrete, which gives an infinite (in theory) set of coordinates. In the above figure, the real world (shown as an aerial photograph) is simplified as a grid where the color of each cell relates to an entity such as a road, highway, or river. For a large grid, the resolution is fine, but at the expense of much larger storage space.

For a small grid, the resolution is coarse but the required storage space is limited. Resolution is an important concern in raster representations. triangles and hexagons), the square is the most commonly used. A raster representation also relies on tessellation: geometric shapes that can completely cover an area.

#Raster and vector data model in gis registration#

This allows for registration with a geographic reference system. Features are divided into cellular arrays and a coordinate (X,Y) is assigned to each cell, as well as a value.

Grid cells are the most common raster representation. Each unit is generally similar in size to another. Based on a cellular organization that divides space into a series of units. Two representational models are dominant raster (grid-based) and vector (line-based): A GIS data model enables a computer to represent real geographical elements as graphical elements. Representing the “real world” in a data model has been a challenge for GIS since their inception in the 1960s.