GEOGRAPHICAL INFORMATION SYSTEM

TOPIC- FEATURE BASED TOPOGRAPHICAL FUNCTION

By- Satya Prakash Dalei

CONTENTSApplications of buffering

Buffering

Applications in buffering

Overlay

Overlay methods

Overlay tools

Applications of overlay

Measuring Distances

Reference

INTRODUCTION GIS analysis is the process to define and execute spatial and attribute procedures to generate derived information.

Spatial analysis uses spatial information to extract new and additional meaning from GIS data which is carried out using a GIS Application having spatial analysis tools for feature statistics or geoprocessing.

Vector data analysis uses the geometric objects of point, line and polygon. And the accuracy of analysis results depends on the accuracy of these objects in terms of location and shape

A number of analytical tools such as Union and Intersect also appear as editing tools performing different functions.

As overlay tools, Union and Intersect work with both spatial and attribute data. But as editing tools, they only work with spatial data (i.e., geometries).

BUFFERING A buffer is a zone around an object, such as a school or intersection, that has some investigative or analytical significance

Buffering usually creates two areas: one area that is within a specified distance to selected real world features and the other area that is beyond. The area that is within the specified distance is called the buffer zone

Features of buffering may be points, lines, or areas

Buffering around points creates circular buffer zones

Buffering around lines creates a series of elongated buffer zones

And buffering around polygons creates buffer zones that extend outward from the polygon boundaries

APPLICATIONS IN BUFFERINGA buffer zone is often treated as a protection zone and is used for planning or regulatory purposes:

A city ordinance may stipulate that no liquor stores or pornographic shops shall be within 1000 feet of a school or a church.

Government regulations may set 2-mile buffer zones along streams to minimize sedimentation from logging operations.

A national forest may restrict oil and gas well drilling within 500 feet of or highways.

A planning agency may set aside land along the edges of streams to study the effects of nutrient, sediment, and pesticide run off, to maintain shade to prevent the rise of stream temperature; and to provide shelter for wildlife and aquatic life

A resource agency may establish stream buffers or vegetated filter strips to protect aquatic resources from adjacent agricultural land-use practices

OVERLAYOverlay is a GIS operation in which layers with a common, registered map base are joined on the basis of their occupation of space

The overlay function creates composite maps by combining diverse data sets

The overlay function can perform simple operations such as laying a road map over a map of local wetlands, or more sophisticated operations such as multiplying and adding map attributes of different value to determine averages and co-occurrencesAn overlay operation is much more than a simple merging of line work; all the attributes of the features taking part in the overlay are carried through, where parcels (polygons) and flood zones (polygons) are overlayed (using the Union tool) to create a new polygon layer. The parcels are split where they are crossed by the flood zone boundary, and new polygons created

OVERLAY METHODSIn general, there are two methods for performing overlay analysis—feature overlay (overlaying points, lines, or polygons) and raster overlay. They are as follows:

Feature Overlay- The overlay function splits features in the input layer where they are overlapped by features in the overlay layer. New areas are created where polygons intersect.

Raster Overlay- In raster overlay, each cell of each layer references the same geographic location. That makes it well suited to combining characteristics for numerous layers into a single layer.

OVERLAY TOOLSThere are two types of overlay tools i.e. raster overlay tools and vector overlay tools. The vector overlay method which are as follows:

APPLICATIONS OF OVERLAYThe overlay output is useful for query and modelling purposes. Some applications are as follows:

The overlay output is useful for query and modelling purposes

Query the areal proportion of each census tract that is within each school district.

Apportion the population for each census tract to school districts according to the areal proportion.

Sum the apportioned population from each census tract for each school district

DISTANCE MEASUREMENT

Distance measurement refers to measuring straight line (Euclidean) distances between features.

Measurements can be made from points in a layer to points in another layer, or from each point in a layer to its nearest point or line in another layer. In both cases, distance measures are stored in a field.

A GIS package such as ArcGlS may include distance measurement as an analysis tool or as a join operation between two tables.

Distance measures can be used directly for data analysis and as inputs to data analysis.

Pattern analysis also uses distance measures as inputs.

REFERENCE

Wikipedia

Introduction to GIS by Kang-tsung-chang

https://web.viu.ca/corrin/GIS/New_Folder/Vector%20Analysis.htm

Grass GIS manual

https://www.esri.com/library/whitepapers/pdfs/arcgis_spatial_analyst.pdf

doc.arcgis.com/en/arcgis-online/get-started

webhelp.esri.com/arcgisdesktop/9.2/index.cfm

guides.library.duke.edu 

Thank You