Desktop Geographic Information System Computer Science Essay

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Geographic Information system (GIS) is a relatively new field and it has started in the 1970's. In Early days computerized GIS was only available to companies and universities that had expensive computer equipments. But technology has evolved surprisingly and these days, anyone with a personal computer or a laptop can use GIS software. GIS Applications have also become much more user friendly than it was in early days. GIS tools are normally programs with a graphical user interface since it is much easier to analyze geographic data in graphical representation.

GIS systems are used in cartography, remote sensing, land surveying, utility management, natural resource management, photogrammetric, geography, urban planning, emergency management, navigation, and localized search engines.

As GIS is a system, it establishes boundaries, purpose or application oriented for which a specific GIS is developed. Hence, a GIS developed for an application, jurisdiction, enterprise, or purpose may not be necessarily interoperable or compatible with a GIS that has been developed for some other application, jurisdiction, enterprise, or purpose. What goes beyond a GIS is a spatial data infrastructure (SDI), a concept that has no such restrictive boundaries.

In a general, the term describes any information system that integrates stores, edits, analyzes, shares, and displays geographic information. In a more generic sense, GIS applications are tools that allow users to create interactive queries, analyze spatial information, edit data, maps, and present the results of all these operations. Geographic information science is the science underlying the geographic concepts, applications and systems, studied in degree and certificate programs at many universities.

Data representation

Data represented in GIS's are real objects such as roads, waterways, trees, elevation, etc. These data can be divided into two main categories.

Discrete objects

Continues objects

In early days there were two methods used to store data in GIS. They are Raster images and Vector. Points, lines and polygons are the attribute references of mapped location. Later on a new hybrid method for storing GIS data introduced. This method stored data which combine three dimensional points with RGB value attached to each point.

Raster

Raster data type represents data with rows and columns of cells which a single value is attached to these cells. There can be an additional value attached to these cells. They can be discrete or continuous as mentioned before. An example for a discrete value can be a GPS location and an example for continues value can be the temperature of particular location. These images are stored in various types of formats such as JPEG, TIF, BLOB, etc. They can be stored in relational database management systems and they can be retrieved quickly if they are indexed. Usually these databases occupied huge amount of space due to size of records.

Vector

Three types of geometry are used to represent different type of geometrical shapes.

Points

Points are used to represent a single point of reference and this is zero dimensions. This cannot be used to do measurements.

Lines or poly lines

Lines or poly lines are used to represent linear features such as road networks, rivers, railroads etc. Line features can measure distance

Polygons

Data representation in this method is Two-dimensional and used for geographical features that cover an area of the earth's surface. Lakes, boundaries, buildings are the example information which can be represented in this method. Measurement of area can be derived from this method.

Categorization of GIS Tool

Desktop GIS

Desktop GISs are used to create, edit, manage, analyze and display geographic data. They are sometimes classified into three functionality categories: GIS Viewer, GIS Editor and GIS Analyst.

Desktop GIS tools allow both armature and pro users to use GIS. For an example a doctor can easily install and use Desktop GIS to a PC and used to record geographic information of patients he consult. If a rate of a specific illness increases, Doctor can check the geographic locations of patients and may be able to find a pattern or the source of the illness.

Quantum GIS

This tool is a user friendly Open Source Geographic Information System which can be used on Linux, UNIX, Mac OSX, and Windows. Quantum GIS supports vector, raster, and database formats. This is licensed under the GNU Public License.

This allows create maps and interactively explore spatial data with a friendly graphical user interface. There are many helpful tools available in the GUI, such as:

Raster and vector support

Extensible plug-in architecture

Digitizing tools

Print composer

Python language bindings

Overview panel

Spatial bookmarks

Identify/Select features

Edit/View attributes

Feature labeling

On the fly projection

 http://gallery.osgeo.org/images/QGIS_screen.png

Figure 1. Screen shot of Quantum GIS

SAGA GIS

SAGA (System for Automated Geo-scientific Analyses) is a free and open source geographic information system used for editing spatial data. SAGA GIS is software with the purpose to give scientists an effective but easily learnable platform for the implementation of geo-scientific methods. This is done by an API. SAGA has a fast growing set of geo-scientific methods, bundled in changeable module libraries.

File access

Interfaces to various table, vector, image and grid file formats

Gridding

Interpolation from vector data using triangulation, nearest neighbor, inverse distance

Geo-statistics

Residual analysis, single and multiple regression analysis, variance analysis

Grid calculator

Combine grids through user defined functions

Grid tools

Merging, re-sampling, gap filling

Image classification

Cluster analysis, box classification, maximum likelihood, pattern recognition, region growing

Projections

Various coordinate transformations for vector and grid data, geo-referencing of grids.

Terrain analysis

Slope, aspect, curvatures, curvature classification, analytical hill shading, sink elimination, flow path analysis, catchment delineation, solar radiation, channel lines, relative altitudes 

Spatial database management systems

PostGIS

PostGIS is an open source tool that adds support for geographic objects to the PostgreSQL object-relational database. This tool supports Geometry types for points, line strings, polygons, multi points, multiline strings, multi polygons and geometry collections. Implementation of this tool based on "light-weight" geometries and indexes optimized to reduce disk and memory footprint. Using light-weight geometries helps servers to increase the amount of data migrated up from physical disk storage into RAM, improving query performance substantially.

The first version was released in 2001 under the GNU General Public License. A stable "1.0" version was released on April 19, 2005, which followed 6 releases candidates. In 2006, PostGIS was certified as a compliant Simple Features for SQL database by the Open Geospatial Consortium.

Features provided by PostGIS

Geometry types for points, line strings, polygons, multi points, multi line strings, multi polygons and geometry collections

Spatial predicates for determining the interactions of geometries using the 3x3 Egenhofer matrix

Spatial operators for determining geospatial measurements like area, distance, length and perimeter

Spatial operators for determining geospatial set operations, like union, difference, symmetric difference and buffers

R-tree-over-GIST spatial indexes for high speed spatial querying

Index selectivity support, to provide high performance query plans for mixed spatial/non-spatial queries

For raster data, under development PostGIS WKT Raster

http://www.paolocorti.net/public/wordpress/wp-content/uploads/2007/02/ziggisinterface.jpg

Figure 2. PostGIS

TerraLib

TerraLib is an open source GIS software library which extends object-relational database management system technology to handle spatiotemporal data types. The library supports different DBMS, including MySQL, PostgreSQL, and Oracle. Its vector data model is upwards compliant with OGC standards. TerraLib supports the development of geographical applications using spatial databases.

Features provided by PostGIS

Included support for layer edition timestamp and theme creation timestamp. This implies a change in the TerraLib database model, which means that existent databases will be converted to new format, by TerraView application

Included support to accept datetime TIFF rasters

Included new methods for projections conversion

WebMap Servers

Web mapping is the process of designing, implementing, generating and delivering maps for internet. While web mapping primarily deals with technological issues, web cartography additionally studies theoretic aspects, the use of web maps, the evaluation and optimization of techniques and workflows, the usability of web maps, social aspects, and more. There are several of products available to use as webmap servers.

Mapnik

This is an open source mapping toolkit which is written in C++.This is useful for both desktop and server based map rendering. Mapnik now also has a powerful rendering backend. When it comes to handling common software tasks such as memory management, file system access, regular expressions, and XML parsing, Mapnik utilizes the Boost C++ Libraries.

http://trac.mapnik.org/raw-attachment/wiki/MapnikViewer/mapnik_viewer.png

Figure 3. Mapnik

GeoServer

GeoServer is an open source software server written in Java that allows users to share and edit geospatial data. Designed for interoperability, it publishes data from any major spatial data source using open standards.

GeoServer reads a variety of data formats and these are considers as features of GeoServer

PostGIS

Oracle Spatial

ArcSDE

DB2

MySQL

Shapefiles

GeoTIFF

GTOPO30

ECW, MrSID

JPEG2000

../../_images/web-admin.png

Figure 4. GeoServer

Google Earth and GIS

One of the smartest geographic information visualization software is Google earth. Google earth is capable of showing earth terrain, building and popular land marks in 3D graphics. It is possible to import GIS data into Google Earth and these data can be used as part of Google Earth visualizations. In Google Earth Pro version it is possible to import many kinds of GIS data directly. Even for the free version of Google Earth, there are other tools for converting GIS data to KML format which can be imported to free version of Google.

Figure 4. Google Earth and GIS

Conclusion

By looking into the evolution of GIS tools, we can observe significant improvements of the quality and the user friendliness. There are plenty of open source GIS tools available for most of platforms and users can try them by downloading and installing them. As a community it would be a lot helpful if useful geographic information is available for public for educational purposes. This field is much more interesting than others as this interact with the real word object those intangible business logics. Features and capabilities of GIS will be improved in the future with the improvements of computer hardware and database management systems.

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