The two broadest classes of sensors are Passive (energy leading to radiation received comes from an external source, e.g., the Sun; the MSS is an example) and Active (energy generated from within the sensor system is beamed outward, and the fraction returned is measured; radar is an example). Sensors can be non-imaging (measures the radiation received from all points in the sensed target, integrates this, and reports the result as an electrical signal strength or some other quantitative attribute, such as radiance) or imaging (the electrons released are used to excite or ionize a substance like silver (Ag) in film or to drive an image producing device like a TV or computer monitor or a cathode ray tube or oscilloscope or a battery of electronic detectors (see further down this page for a discussion of detector types); since the radiation is related to specific points in the target, the end result is an image [picture] or a raster display [for example: the parallel horizontal lines on a TV screen]).
Radiometer is a general term for any instrument that quantitatively measures the EM radiation in some interval of the EM spectrum. When the radiation is light from the narrow spectral band including the visible, the term photometer can be substituted. If the sensor includes a component, such as a prism or diffraction grating, that can break radiation extending over a part of the spectrum into discrete wavelengths and disperse (or separate) them at different angles to an array of detectors, it is called a spectrometer. One type of spectrometer (used in the laboratory for chemical analysis) passes multiwavelength radiation through a slit onto a dispersing medium which reproduces the slit as lines at various spacings on a film plate (discussed on page I-2a). The term spectroradiometer is reserved for sensors that collect the dispersed radiation in bands rather than discrete wavelengths. Most air/space sensors are spectroradiometers.
Sensors that instantaneously measure radiation coming from the entire scene at once are called framing systems. The eye, a photo camera, and a TV vidicon belong to this group. The size of the scene that is framed is determined by the apertures and optics in the system that define the field of view, or FOV. If the scene is sensed point by point (equivalent to small areas within the scene) along successive lines over a finite time, this mode of measurement makes up a scanning system. Most non-camera sensors operating from moving platforms image the scene by scanning.
Saturday, January 19, 2008
Remote Sensing Tutorial
Sensor Technology; Types of Resolution
So far, we have considered mainly the nature and characteristics of EM radiation in terms of sources and behavior when interacting with materials and objects. It was stated that the bulk of the radiation sensed is either reflected or emitted from the target, generally through air until it is monitored by a sensor. The subject of what sensors consist of and how they perform (operate) is important and wide ranging. It is also far too involved to merit an extended treatment in this Tutorial. However, a synopsis of some of the basics is warranted on this page. A comprehensive overall review of Sensor Technology, developed by the Japanese Association of Remote Sensing, is found on the Internet at this mirror site. Some useful links to sensors and their applications is included in this NASA site. We point out here that many readers of this Tutorial are now using a sophisticated sensor that uses some of the technology described below: the Digital Camera; more is said about this everyday sensor near the bottom of the page.
Most remote sensing instruments (sensors) are designed to measure photons. The fundamental principle underlying sensor operation centers on what happens in a critical component - the detector. This is the concept of the photoelectric effect (for which Albert Einstein, who first explained it in detail, won his Nobel Prize [not for Relativity which was a much greater achievement]; his discovery was, however, a key step in the development of quantum physics). This, simply stated, says that there will be an emission of negative particles (electrons) when a negatively charged plate of some appropriate light-sensitive material is subjected to a beam of photons. The electrons can then be made to flow as a current from the plate, are collected, and then counted as a signal. A key point: The magnitude of the electric current produced (number of photoelectrons per unit time) is directly proportional to the light intensity. Thus, changes in the electric current can be used to measure changes in the photons (numbers; intensity) that strike the plate (detector) during a given time interval. The kinetic energy of the released photoelectrons varies with frequency (or wavelength) of the impinging radiation. But, different materials undergo photoelectric effect release of electrons over different wavelength intervals; each has a threshold wavelength at which the phenomenon begins and a longer wavelength at which it ceases.
So far, we have considered mainly the nature and characteristics of EM radiation in terms of sources and behavior when interacting with materials and objects. It was stated that the bulk of the radiation sensed is either reflected or emitted from the target, generally through air until it is monitored by a sensor. The subject of what sensors consist of and how they perform (operate) is important and wide ranging. It is also far too involved to merit an extended treatment in this Tutorial. However, a synopsis of some of the basics is warranted on this page. A comprehensive overall review of Sensor Technology, developed by the Japanese Association of Remote Sensing, is found on the Internet at this mirror site. Some useful links to sensors and their applications is included in this NASA site. We point out here that many readers of this Tutorial are now using a sophisticated sensor that uses some of the technology described below: the Digital Camera; more is said about this everyday sensor near the bottom of the page.
Most remote sensing instruments (sensors) are designed to measure photons. The fundamental principle underlying sensor operation centers on what happens in a critical component - the detector. This is the concept of the photoelectric effect (for which Albert Einstein, who first explained it in detail, won his Nobel Prize [not for Relativity which was a much greater achievement]; his discovery was, however, a key step in the development of quantum physics). This, simply stated, says that there will be an emission of negative particles (electrons) when a negatively charged plate of some appropriate light-sensitive material is subjected to a beam of photons. The electrons can then be made to flow as a current from the plate, are collected, and then counted as a signal. A key point: The magnitude of the electric current produced (number of photoelectrons per unit time) is directly proportional to the light intensity. Thus, changes in the electric current can be used to measure changes in the photons (numbers; intensity) that strike the plate (detector) during a given time interval. The kinetic energy of the released photoelectrons varies with frequency (or wavelength) of the impinging radiation. But, different materials undergo photoelectric effect release of electrons over different wavelength intervals; each has a threshold wavelength at which the phenomenon begins and a longer wavelength at which it ceases.
Friday, January 18, 2008
Remote Sensing
Applied Remote Sensing involves the detecting and measuring of electromagnetic energy (usually photons) emanating from distant objects made of various materials, so that the user can identify and categorize these objects - usually, as rendered into images - by class or type, substance, and spatial distribution. Generally, this more conventional description of remote sensing has a specific criterion by which its products point to this specific use of the term: images much like photos are a main output of the sensed surfaces of the objects of interest. However, the data often can also be shown as "maps" and "graphs", or to a lesser extent, as digital numbers that can be input to computer-based analysis, and in this regard are like the common data displays resulting from geophysical remote sensing. As applied to meteorological remote sensing, both images (e.g., clouds) and maps (e.g., temperature variations) can result; atmospheric studies (especially of the gases in the air, and their properties) can be claimed by both traditionalists and geophysicists.
All of these statements are valid and, taken together, should give you a reasonable insight into the meaning and use of the term "Remote Sensing" but its precise meaning depends on the context in which it is spoken of.
Thus, as the above comments suggest, some technical purists arbitrarily stretch the scope or sphere of remote sensing to include other measurements of physical properties from sources "at a distance" that are more properly included in the general term "Geophysics". (Geophysics has a scientific connotation: it is pertinent to the study of the physical properties of Earth and other planets. It likewise has an applied connotation: it is the technology often used to search for oil and gas and for mineral deposits.) This latter is especially conducted through such geophysical methods as seismic, magnetic, gravitational, acoustical, and nuclear decay radiation surveys. Magnetic and gravitational measurements respond to variations in force fields, so these can be carried out from satellites. Remote sensing, as defined in this context, would be a subset within the branch of science known as Geophysics. However, practitioners of remote sensing, in its narrower meaning, tend to exclude these other areas of Geophysics from their understanding of the meaning implicit in the term.
Still, space systems - mostly on satellites - have made enormous contributions to regional and global geophysical surveys. This is because it is very difficult and costly to conduct ground and aerial surveys over large areas and then to coordinate the individual surveys by joining them together. To obtain coherent gravity and magnetic data sets on a world scale, operating from the global perspective afforded by orbiting satellites is the only reasonable alternate way to provide total coverage.
One could argue that Geophysics deserves a Section of its own but in the remainder of this Tutorial we choose to confine our attention almost entirely to those systems that produce data by measuring in the electromagnetic radiation (EMR) spectrum (principally in the Visible, Infrared, and Radio regions). We will reserve our treatment of Geophysics to three pages near the end of this Introduction. There you are given examples of the use of satellite instruments to obtain information on particles and fields as measured inside and around the Earth; in Sections 19 and 20 (Planets and Cosmology) there will also be some illustrations of several types of geophysical measurements.
One mode of remote sensing not treated in the Tutorial is acoustic monitoring of sound waves in atmospheric and marine environments. For example, volcanic eruptions or nuclear (testing) explosions can be detected by sensitive sound detectors. Sonar is used to track submarines and surface ships in the oceans. Sound through water are also involved in listening to marine animals such as whales and porpoises.
It may seem surprising to realize that going to the doctor can involve remote sensing. Most obvious, on a miniature scale, is listening to a heartbeat using the stethoscope. But in the field of modern medical technology, powerful, often large, instruments such as CATscans and Magnetic Resonance Imaging, are now almost routinely used for non-invasive subskin investigation of human tissue and organs. This is indeed another major application of remote sensing that will be surveyed on pages I-26c through I-26e.
The traditional way to start consideration of what remote sensing is and means is to set forth its underlying principles in a chapter devoted to the Physics on which remote sensing is founded. This will be done in the next 5 pages. The ideas developed may seem arcane. These pages contain the "technical jargon" that remote sensing specialists like to banter about. With this caveat in mind, work through the pages, try to understand the esoteric, and commit to memory what seems useful.
All of these statements are valid and, taken together, should give you a reasonable insight into the meaning and use of the term "Remote Sensing" but its precise meaning depends on the context in which it is spoken of.
Thus, as the above comments suggest, some technical purists arbitrarily stretch the scope or sphere of remote sensing to include other measurements of physical properties from sources "at a distance" that are more properly included in the general term "Geophysics". (Geophysics has a scientific connotation: it is pertinent to the study of the physical properties of Earth and other planets. It likewise has an applied connotation: it is the technology often used to search for oil and gas and for mineral deposits.) This latter is especially conducted through such geophysical methods as seismic, magnetic, gravitational, acoustical, and nuclear decay radiation surveys. Magnetic and gravitational measurements respond to variations in force fields, so these can be carried out from satellites. Remote sensing, as defined in this context, would be a subset within the branch of science known as Geophysics. However, practitioners of remote sensing, in its narrower meaning, tend to exclude these other areas of Geophysics from their understanding of the meaning implicit in the term.
Still, space systems - mostly on satellites - have made enormous contributions to regional and global geophysical surveys. This is because it is very difficult and costly to conduct ground and aerial surveys over large areas and then to coordinate the individual surveys by joining them together. To obtain coherent gravity and magnetic data sets on a world scale, operating from the global perspective afforded by orbiting satellites is the only reasonable alternate way to provide total coverage.
One could argue that Geophysics deserves a Section of its own but in the remainder of this Tutorial we choose to confine our attention almost entirely to those systems that produce data by measuring in the electromagnetic radiation (EMR) spectrum (principally in the Visible, Infrared, and Radio regions). We will reserve our treatment of Geophysics to three pages near the end of this Introduction. There you are given examples of the use of satellite instruments to obtain information on particles and fields as measured inside and around the Earth; in Sections 19 and 20 (Planets and Cosmology) there will also be some illustrations of several types of geophysical measurements.
One mode of remote sensing not treated in the Tutorial is acoustic monitoring of sound waves in atmospheric and marine environments. For example, volcanic eruptions or nuclear (testing) explosions can be detected by sensitive sound detectors. Sonar is used to track submarines and surface ships in the oceans. Sound through water are also involved in listening to marine animals such as whales and porpoises.
It may seem surprising to realize that going to the doctor can involve remote sensing. Most obvious, on a miniature scale, is listening to a heartbeat using the stethoscope. But in the field of modern medical technology, powerful, often large, instruments such as CATscans and Magnetic Resonance Imaging, are now almost routinely used for non-invasive subskin investigation of human tissue and organs. This is indeed another major application of remote sensing that will be surveyed on pages I-26c through I-26e.
The traditional way to start consideration of what remote sensing is and means is to set forth its underlying principles in a chapter devoted to the Physics on which remote sensing is founded. This will be done in the next 5 pages. The ideas developed may seem arcane. These pages contain the "technical jargon" that remote sensing specialists like to banter about. With this caveat in mind, work through the pages, try to understand the esoteric, and commit to memory what seems useful.
Rural Settlements
The basic human needs are food, clothing, and shelter. Of these, buildings reveal the most about a culture and those who build them, as a visible expression of the culture. When large permanent settlements evolved buildings became more substantial, specialized, and permanent. As culture became more complex the simple practicality of adaptation to, and protection from, the elements was expanded to include functional differentiation, reflecting the changing needs of people and culture.
Where People Live
Early humans all lived in “rural” areas. They were few in numbers and generally mobile. It was not until the development of agriculture that “permanent” settlements became the norm. As recently as several hundred years ago the vast majority of humans still resided in rural areas, generally in agricultural villages raising crops or livestock to support themselves. Towns and cities were few and the exception rather than the norm. It was a very different world than residents of modem, technically advanced cultures experience today.
In the late l990s, about half the world’s population still resides in rural areas. This is because the vast majority of humanity still farms the land, often in ways that have not changed significantly. In portions of East and South Asia as many as three out of four residents may live in a rural area. By contrast, in the United States, Canada, Western European countries, Japan, and Australia there are far more urban than rural dwellers, reflecting changes in industrialization, transportation, and urbanization over the last 100 years.
Rural Dwellings
The cultural landscape is the human imprint on the Earths surface, and no human activity produces a more visible cultural landscape than agriculture. Much can be learned about a culture by observing rural settlement patterns. The forms, functions, building materials, and the spacing of rural dwellings reveal much about a region and its culture. The compact, crowded agricultural villages of India, for example, designed to conserve land for actual farming, stand in sharp contrast to the widely scattered individual farmsteads of the American Great Plains where more land may be actually occupied by buildings on each farm than the Indian farmer has for cultivation.
Social and economic opportunities and needs, natural environments, and traditions are also cultural characteristics that are revealed in the rural settlement scene. Large, elaborate dwellings reflect prosperity or social standing while a church, temple or other place of worship reveals something about the priorities of the culture. Dwellings may be concentrated along and near a road or waterway, suggesting available transportation, on high ground suggesting concern about frequent flooding, or on, say, southern slopes reflecting concerns about the winter months (this could also indicate a location in the Northern Hemisphere).
Building Materials
Except in the wealthier societies, most humans construct their dwellings of whatever local material is available commensurate with their experience and the natural environment. Wattle, wood, brick, and stone are among the building materials used in domestic architecture. The selection of the building material is also an indication of the climate of the region. Traditional rural societies are not wealthy and therefore cannot afford, for example, to import wood from great distances if it is not immediately available locally.
Log houses require considerable labor, to say nothing of available timber and transportation needs. They usually indicate a period of severe winter. Cut wood (lumber) is not immediately available in many areas and is expensive. The appearance of elaborate wood or brick dwellings in a region such as the North American Great Plains indicates wealth and an elaborate transportation system. Stone is a common building material if available locally and has great durability. Like wood, its appearance in the dwellings of a region considerably removed from local supplies indicates something about the affluence and social standing of the culture and its inhabitants.
Settlement Patterns
The form or layout of rural villages reflect historical circumstances, the nature of the land, and economic conditions. They range from linear and clustered to circular and grid pattern. Each has something to say about the culture that built them.
Early villages had to be near a reliable water supply, be defensible, and have sufficient land nearby for cultivation to name but a few concerns. They also had to adapt to local physical and environmental conditions, conditions which can be identified with a practiced eye. In Nepal in the Himalayan Mountains, villages cling to the slopes above the river bottoms, indicating awareness of spring floods with the melting of winter snows. Villages in the Netherlands are linear, crowded on the dikes surrounding land reclaimed from the sea. Grid-patterned villages in much of Latin America reflect the influence of their Spanish founders while circular villages in parts of Africa indicate a need for a safe haven for livestock at night. A careful examination of the rural settlement of a region reveals much about the culture, its history and traditions.
Where People Live
Early humans all lived in “rural” areas. They were few in numbers and generally mobile. It was not until the development of agriculture that “permanent” settlements became the norm. As recently as several hundred years ago the vast majority of humans still resided in rural areas, generally in agricultural villages raising crops or livestock to support themselves. Towns and cities were few and the exception rather than the norm. It was a very different world than residents of modem, technically advanced cultures experience today.
In the late l990s, about half the world’s population still resides in rural areas. This is because the vast majority of humanity still farms the land, often in ways that have not changed significantly. In portions of East and South Asia as many as three out of four residents may live in a rural area. By contrast, in the United States, Canada, Western European countries, Japan, and Australia there are far more urban than rural dwellers, reflecting changes in industrialization, transportation, and urbanization over the last 100 years.
Rural Dwellings
The cultural landscape is the human imprint on the Earths surface, and no human activity produces a more visible cultural landscape than agriculture. Much can be learned about a culture by observing rural settlement patterns. The forms, functions, building materials, and the spacing of rural dwellings reveal much about a region and its culture. The compact, crowded agricultural villages of India, for example, designed to conserve land for actual farming, stand in sharp contrast to the widely scattered individual farmsteads of the American Great Plains where more land may be actually occupied by buildings on each farm than the Indian farmer has for cultivation.
Social and economic opportunities and needs, natural environments, and traditions are also cultural characteristics that are revealed in the rural settlement scene. Large, elaborate dwellings reflect prosperity or social standing while a church, temple or other place of worship reveals something about the priorities of the culture. Dwellings may be concentrated along and near a road or waterway, suggesting available transportation, on high ground suggesting concern about frequent flooding, or on, say, southern slopes reflecting concerns about the winter months (this could also indicate a location in the Northern Hemisphere).
Building Materials
Except in the wealthier societies, most humans construct their dwellings of whatever local material is available commensurate with their experience and the natural environment. Wattle, wood, brick, and stone are among the building materials used in domestic architecture. The selection of the building material is also an indication of the climate of the region. Traditional rural societies are not wealthy and therefore cannot afford, for example, to import wood from great distances if it is not immediately available locally.
Log houses require considerable labor, to say nothing of available timber and transportation needs. They usually indicate a period of severe winter. Cut wood (lumber) is not immediately available in many areas and is expensive. The appearance of elaborate wood or brick dwellings in a region such as the North American Great Plains indicates wealth and an elaborate transportation system. Stone is a common building material if available locally and has great durability. Like wood, its appearance in the dwellings of a region considerably removed from local supplies indicates something about the affluence and social standing of the culture and its inhabitants.
Settlement Patterns
The form or layout of rural villages reflect historical circumstances, the nature of the land, and economic conditions. They range from linear and clustered to circular and grid pattern. Each has something to say about the culture that built them.
Early villages had to be near a reliable water supply, be defensible, and have sufficient land nearby for cultivation to name but a few concerns. They also had to adapt to local physical and environmental conditions, conditions which can be identified with a practiced eye. In Nepal in the Himalayan Mountains, villages cling to the slopes above the river bottoms, indicating awareness of spring floods with the melting of winter snows. Villages in the Netherlands are linear, crowded on the dikes surrounding land reclaimed from the sea. Grid-patterned villages in much of Latin America reflect the influence of their Spanish founders while circular villages in parts of Africa indicate a need for a safe haven for livestock at night. A careful examination of the rural settlement of a region reveals much about the culture, its history and traditions.
Thursday, January 17, 2008
What is GIS
The key word to this technology is Geography - this usually means that the data (or at least some proportion of the data) is spatial, in other words, data that is in some way referenced to locations on the earth. Coupled with this data is usually data known as attribute data. Attribute data generally defined as additional information, which can then be tied to spatial data. An example of this would be schools. The actual location of the schools is the spatial data. Additional data such as the school name, level of education taught, school capacity would make up the attribute data. It is the partnership of these two data types that enables GIS to be such an effective problem solving tool.
GIS operates on many levels. On the most basic level, GIS is used as computer cartography, i.e. mapping. The real power in GIS is through using spatial and statistical methods to analyze attribute and geographic information. The end result of the analysis can be derivative information, interpolated information or prioritized information.
“In the strictest sense, a GIS is a computer system capable of assembling, storing, manipulating, and displaying geographically referenced information, i.e. data identified according to their locations. Practitioners also regard the total GIS as including operating personnel and the data that go into the system.” USGS“A geographic information system (GIS) is a computer-based tool for mapping and analyzing things that exist and events that happen on earth. GIS technology integrates common database operations such as query and statistical analysis with the unique visualization and geographic analysis benefits offered by maps.” ESRI
“GIS is an integrated system of computer hardware, software, and trained personnel linking topographic, demographic, utility, facility, image and other resource data that is geographically referenced.” NASAGIS has already affected most of us in some way without us even realizing it. If you’ve ever using an Internet mapping program to find directions, congratulations, you’ve personally used GIS. The new supermarket chain on the corner was probably located using GIS to determine the most effective place to meet customer demand.Components of GIS
This article has briefly explained what GIS is. The next step in understanding GIS is to look at each component of GIS and how they work together. These components are:
Hardware
Hardware comprises the equipment needed to support the many activities of GIS ranging from data collection to data analysis. The central piece of equipment is the workstation, which runs the GIS software and is the attachment point for ancillary equipment. Data collection efforts can also require the use of a digitizer for conversion of hard copy data to digital data and a GPS data logger to collect data in the field. The use of handheld field technology is also becoming an important data collection tool in GIS. With the advent of web-enabled GIS, web servers have also become an important piece of equipment for GIS.
Software
Different software packages are important for GIS. Central to this is the GIS application package. Such software is essential for creating, editing and analyzing spatial and attribute data, therefore these packages contain a myriad of GIS functions inherent to them. Extensions or add-ons are software that extends the capabilities of the GIS software package. For example, Xtools is an ArcView extension that adds more editing capabilities to ArcView 3.x. Component GIS software is the opposite of application software. Component GIS seeks to build software applications that meet a specific purpose and thus are limited in their spatial analysis capabilities. Utilities are stand-alone programs that perform a specific function. For example, a file format utility that converts from on type of GIS file to another. There is also web-GIS software that helps serve data through Internet browsers.
Data
Data is the core of any GIS. There are two primary types of data that are used in GIS. A geodatabase is a database that is in some way referenced to locations on the earth. Geodatabases are grouped into two different types: vector and raster. Coupled with this data is usually data known as attribute data. Attribute data generally defined as additional information, which can then be tied to spatial data. Documentation of GIS datasets is known as metadata.
People
Well-trained people knowledgeable in spatial analysis and skilled in using GIS software are essential to the GIS process. There are three factors to the people component: education, career path, and networking. The right education is key; taking the right combination of classes. Selecting the right type of GIS job is important. A person highly skilled in GIS analysis should not seek a job as a GIS developer if they haven’t taken the necessary programming classes. Finally, continuous networking with other GIS professionals is essential for the exchange of ideas as well as a support community.
GIS operates on many levels. On the most basic level, GIS is used as computer cartography, i.e. mapping. The real power in GIS is through using spatial and statistical methods to analyze attribute and geographic information. The end result of the analysis can be derivative information, interpolated information or prioritized information.
“In the strictest sense, a GIS is a computer system capable of assembling, storing, manipulating, and displaying geographically referenced information, i.e. data identified according to their locations. Practitioners also regard the total GIS as including operating personnel and the data that go into the system.” USGS“A geographic information system (GIS) is a computer-based tool for mapping and analyzing things that exist and events that happen on earth. GIS technology integrates common database operations such as query and statistical analysis with the unique visualization and geographic analysis benefits offered by maps.” ESRI
“GIS is an integrated system of computer hardware, software, and trained personnel linking topographic, demographic, utility, facility, image and other resource data that is geographically referenced.” NASAGIS has already affected most of us in some way without us even realizing it. If you’ve ever using an Internet mapping program to find directions, congratulations, you’ve personally used GIS. The new supermarket chain on the corner was probably located using GIS to determine the most effective place to meet customer demand.Components of GIS
This article has briefly explained what GIS is. The next step in understanding GIS is to look at each component of GIS and how they work together. These components are:
Hardware
Hardware comprises the equipment needed to support the many activities of GIS ranging from data collection to data analysis. The central piece of equipment is the workstation, which runs the GIS software and is the attachment point for ancillary equipment. Data collection efforts can also require the use of a digitizer for conversion of hard copy data to digital data and a GPS data logger to collect data in the field. The use of handheld field technology is also becoming an important data collection tool in GIS. With the advent of web-enabled GIS, web servers have also become an important piece of equipment for GIS.
Software
Different software packages are important for GIS. Central to this is the GIS application package. Such software is essential for creating, editing and analyzing spatial and attribute data, therefore these packages contain a myriad of GIS functions inherent to them. Extensions or add-ons are software that extends the capabilities of the GIS software package. For example, Xtools is an ArcView extension that adds more editing capabilities to ArcView 3.x. Component GIS software is the opposite of application software. Component GIS seeks to build software applications that meet a specific purpose and thus are limited in their spatial analysis capabilities. Utilities are stand-alone programs that perform a specific function. For example, a file format utility that converts from on type of GIS file to another. There is also web-GIS software that helps serve data through Internet browsers.
Data
Data is the core of any GIS. There are two primary types of data that are used in GIS. A geodatabase is a database that is in some way referenced to locations on the earth. Geodatabases are grouped into two different types: vector and raster. Coupled with this data is usually data known as attribute data. Attribute data generally defined as additional information, which can then be tied to spatial data. Documentation of GIS datasets is known as metadata.
People
Well-trained people knowledgeable in spatial analysis and skilled in using GIS software are essential to the GIS process. There are three factors to the people component: education, career path, and networking. The right education is key; taking the right combination of classes. Selecting the right type of GIS job is important. A person highly skilled in GIS analysis should not seek a job as a GIS developer if they haven’t taken the necessary programming classes. Finally, continuous networking with other GIS professionals is essential for the exchange of ideas as well as a support community.
Wednesday, January 16, 2008
join my group
join my group and discuss about highways and settlement
http://in.groups.yahoo.com/group/highway-settlements/join
http://in.groups.yahoo.com/group/highway-settlements/join
What is GIS? : GIS Lounge - Geographic Information Systems
It is a rapidly growing technological field that incorporates graphical features with tabular data in order to assess real-world problems. What is now the GIS field began around 1960, with the discovery that maps could be programmed using simple code and then stored in a computer allowing for future modification when necessary. This was a welcome change from the era of hand cartography when maps had to be painstakingly created by hand; even small changes required the creation of a new map. The earliest version of a GIS was known as computer cartography and involved simple linework to represent land features. From that evolved the concept of overlaying different mapped features on top of each other to determine patterns and causes of spatial phenomenon.
The capabilities of GIS are a far cry from the simple beginnings of computer cartography. At the simplest level, GIS can be thought of as a high-tech equivalent of a map. However, not only can paper maps be produced far quicker and more efficiently, the storage of data in an easily accessible digital format enables complex analysis and modeling not previously possible. The reach of GIS expands into all disciplines and has been used for such widely ranged problems as prioritizing sensitive species habitat to determining optimal real estate locations for new businesses.
The capabilities of GIS are a far cry from the simple beginnings of computer cartography. At the simplest level, GIS can be thought of as a high-tech equivalent of a map. However, not only can paper maps be produced far quicker and more efficiently, the storage of data in an easily accessible digital format enables complex analysis and modeling not previously possible. The reach of GIS expands into all disciplines and has been used for such widely ranged problems as prioritizing sensitive species habitat to determining optimal real estate locations for new businesses.
Urban Population
Urban populations in India are concentrated in the six most developed state Maharashtra, Gujarat, Tamil Nadu, Karnataka, West Bengal and Punjab where rates of urbanisation remained the same or increased during the 1990s. On the other hand urbanisation rates slowed in the backward states of Bihar, Madhya Pradesh, Rajasthan and Uttar Pradesh (the “BIMARU” states). Overall, there has been a slowing in the growth rate of urban populations from the record level of 3.8% per annum in the 1970s, to 3.1% in the 1980s and further to 2.7% in the 1990s, and the slowing has been greater in the smaller towns .
Subscribe to:
Posts (Atom)