Vector Vector Data Structure Vector data represents features as points, lines, and polygons. A point feature is an x and y coordinate, a line is a string of consecutive points, and a polygon is a string of consecutive points that closes back upon itself. Vector data sets can have topology (see section 3.5). Topology means that, in addition to the position of every feature, the software maintains the spatial relationships of adjacency ... Read More »

## Category Archives: GIS

Feed Subscription## Raster Data Structure

Raster Raster Data Structure This type of data is based on a uniform grid of cells or pixels that represent an area of interest.Individual cells can be identified by the row andcolumn they occupy. Each cell is by definition A homogeneous unit with respect to its attributes. This data formats are used in satellite imagery and Raster based GIS packages such as Grass, IDRISI, Sage, UNIX ARC/INFO, ... Read More »

## Map Scale

Map Scale A ratio of reduction between real world distances and distances on a map is called Map Scale. The following three statements show the same scale: 1 inch = 2,000 feet 1 inch = 24,000 inches 1:24,000 The left side of the ratio is the distance on the map and the right side of the ratio is the distance on thesurface of the ... Read More »

## Topology

Topology Topology is a data structure often used in GIS. Topology is the stored relationships between map features. When topology has been created (such as in an ARC/INFO coverage), the file would “know” its position, “know” what is around it, “understand” its environment by virtue of recognizing its surroundings, and “know” how to get from A to B. Topological relationships are stored ... Read More »

## Latitude-longitude

Latitude-longitude Latitude-longitude is not a two-dimensional coordinate system but is commonly referred to as one. Lines of latitude run east west parallel to the equator. Longitude lines run north-south and converge at the poles. Therefore, the length of one degree of longitude varies depending upon the latitude at which it is measured. For example, one degree of longitude at the equator ... Read More »

## UTM

Universal Transverse Mercator (UTM) Although UTM is technically a projection and NOT a coordinate system, it is commonly referred to as a coordinate system. This is because it is a set of zones with altered offsets and is based on the Transverse Mercator projection. It is used on the United States Geologic Survey (USGS) Topographic maps. It Units must be in feet or meters, but is most often in ... Read More »

## Coordinate

Coordinate The following coordinate systems that are mostly used now a days Latitude-longitude Latitude-Longitude is not a two-dimensional coordinate system but is commonly referred to as one. Lines of latitude run east west parallel to the equator. Longitude lines run north-south and converge at the poles. Therefore, the length of one degree of longitude varies depending upon the latitude at which it ... Read More »

## Maps

Maps Coordinate Systems in Maps Coordinate systems are comprised of spheroids, datum, and projections, and are specified in terms of units (i.e., feet, meters, yards, etc.). Coordinate systems locate features by x and y coordinates in the maps. Spheroids in Maps A spheroid is a mathematical description of the earth. Over time these mathematical expressions have changed from describing the ... Read More »