GIS and Remote Sensing_BSC

Introduction: A geographic information system (GIS) is a computer system for capturing, storing, checking, and displaying data related to positions on Earth’s surface. GIS can show many different kinds of data on one map, such as streets, buildings, vegetation types, population characteristic, and economic development. This enables people to more easily see, analyze, and understand patterns and relationships.

 GIS software are GRASS GIS, gvSIG, JUMP GIS, Capaware, Autodesk etc.

Advantages of GIS

1.      Cost saving from greater efficiency: These are associated either with carrying out the mission (i.e., labor savings from automating or improving a workflow) or improvements in the mission itself.   A good case for both of these is Sears, which implemented GIS in its logistics operations and has seen dramatic improvements.  Sears considerably reduced the time it takes for dispatchers to create routes for their home delivery trucks (by about 75%).  It also benefited enormously in reducing the costs of carrying out the mission. Sears also improved customer service, reduced the number of return visits to the same site, and scheduled appointments more efficiently.

2.      Improved communication: GIS-based maps and visualizations greatly assist in understanding situations.  They are a new language that improves communication between different teams, departments, disciplines, professional fields, organizations, and the public.

3.      Better Decision Making: This typically has to do with making better decisions about location.  Common examples include real estate site selection, route/corridor selection, planning, conservation, natural resource extraction, etc.  People are beginning to realize that making the correct decision about a location is strategic to the success of an organization.

4.      Better record keeping: Many organizations have a primary responsibility of maintaining records about the status and change of geography.  Cultural geography examples are zoning, population census, land ownership, and administrative boundaries.  Physical geography examples include forest inventories, biological inventories, environmental measurements, water flows, and a whole host of geographic accountings.  GIS provides a strong framework for managing these types of systems with full transaction support and reporting tools. 

5.      Managing geographically: In government and many large corporations, GIS is becoming essential to understand what is going on.  Senior administrators and executives at the highest levels of government use GIS information products to communicate.  These products provide a visual framework for conceptualizing, understanding, and action.  Examples briefings about various geographic patterns and relationships including land use, crime, the environment, and defense/security situations.  Examples in the private sector include most utilities, forestry and oil companies, and most commercial/retail businesses. 

Disadvantages

• Very expensive.
• Requires enormous amount of date: makes it prone for error.
• Geographical error increases with larger scale.
• Relative loss of resolution.
• Violation of privacy.

Remote sensing: Remote sensing is the science of obtaining information about objects or areas from a distance, typically from aircraft or satellites. Remote sensors collect data by detecting the energy that is reflected from Earth.

Remote sensors can be either passive or active. Passive sensors respond to external stimuli. They record natural energy that is reflected or emitted from the Earth's surface. The most common source of radiation detected by passive sensors is reflected sunlight.

In contrast, active sensors use internal stimuli to collect data about Earth. For example, a laser-beam remote sensing system projects a laser onto the surface of Earth and measures the time that it takes for the laser to reflect back to its sensor.

Remote sensing has a wide range of applications in many different fields:

·        Coastal applications: Monitor shoreline changes, track sediment transport, and map coastal features. Data can be used for coastal mapping and erosion prevention.

·        Ocean applications: Monitor ocean circulation and current systems, measure ocean temperature and wave heights, and track sea ice. Data can be used to better understand the oceans and how to best manage ocean resources.

·        Hazard assessment: Track hurricanes, earthquakes, erosion, and flooding. Data can be used to assess the impacts of a natural disaster and create preparedness strategies to be used before and after a hazardous event.

·        Natural resource management: Monitor land use, map wetlands, and chart wildlife habitats. Data can be used to minimize the damage that urban growth has on the environment and help decide how to best protect natural resources.

Who uses remote sensing and why

Geographer- who looks for change on Earth's surface that needs to be mapped.

Forester- who needs information about what type of trees is growing and how they have been affected by disease, fire, pollution.

Environmentalist- who want to detect, indentify and follow the movement of pollutants such as oil slick on the ocean.

Geologist- who is interested in finding valuable minerals

Farmer-who wants to track of his crops, how they are affected by drought, floods, disease or pests

Ship captain- who needs to find the best route.

Firefighter-  sends out his crews based on the information about the size and movement of a forest fire.

History Development of GIS:

Stated primarily in 1832 by French geographer Charles Picquet when he applied spatial analysis in epidemiology.

Canada developed the first and really operational GIS called Canada Geographical Information System (CGIS) and was being used in 1960 to save, manipulate and study the data gather for Canada Land Inventory.

There have been four distinct phases in the development of Geographical Information System.

Phase one- between early 1960s and mid 1970s saw a new discipline being dominated by a few individual who were to sharp the direction of future research and development.

Phase two- from mid 1970 to early 1980s saw the adoption of technologies by natural agencies that led to a focus on the development of best practice.

Phase three- between 1980to late 1982s saw the development and exploitation of the commercial market place surrounding GIS

Phasa four- since late 1980s has seen a focus on way of improving the usability of technology by making facilities more user centric.

Component of GIS (GIS physical Components): A working GIS has five key components: hardware, software, data, people, and methods.

Hardware:  Hardware is the computer on which a GIS operates. Today, GIS software runs on a wide range of hardware types, from centralized computer servers to desktop computers used in stand-alone or networked configurations.

Software:GIS software provides the functions and tools needed to store, analyze, and display geographic information. Key software components are

·        Tools for the input and manipulation of geographic information

·        A database management system (DBMS)

·        Tools that support geographic query, analysis, and visualization

·        A graphical user interface (GUI) for easy access to tools

Data: The most important component of a GIS is the data. Geographic data and related tabular data can be collected in-house or purchased from a commercial data provider. A GIS will integrate spatial data with other data resources and can even use a DBMS, used by most organizations to organize and maintain their data, to manage spatial data.

People: GIS technology is of limited value without the people who manage the system and develop plans for applying it to real-world problems. GIS users range from technical specialists who design and maintain the system to those who use it to help them perform their everyday work.

Methods: A successful GIS operates according to a well-designed plan and business rules, which are the models and operating practices unique to each organization.

 

GIS functional components: GIS has four main functional components or subsystem. They are input system, data storage, data manipulation and analysis system and data output system

Data Input: It allows users to capture, collect and transform spatial and thematic data into digital form. Data may be combination of hardcopy maps, aerial photographs, remotely sensed images, reports, survey documents etc.

Data storage and Retrieval: The data storage and retrieval subsystem organizes the data into a form that allows it to be retrieved by the user for analysis and permits data to be quickly retrieved by the used for analysis and permit rapid and accurate updates to be made to Database. This usually involves the use of a database management system.

Data Manipulation and analysis: It allows users to define and execute spatial and attribute procedure to generate derived information.

Data Output: The data output subsystem allows the user to generate graphic displays (maps and charts) and tabular reports.

GIS DATA TYPES: The basic data type in a GIS reflects traditional data found on a map. Accordingly, GIS technology utilizes two basic types of data. These are:

	Spatial data	It describes the absolute and relative location of geographic features. Location information is provided in maps by using points, lines and polygons. These geometric descriptions are the basic data elements of a map.
	Attribute data	This type of data type describes characteristics of the spatial features. These characteristics can be quantitative and/or qualitative in nature. Attribute data is often referred to as tabular data.

Thus, the coordinate location of a forestry stand would be spatial data, while the characteristics of that forestry stand, e.g. cover group, dominant species, crown closure, height, etc., would be attribute data. Other data types, in particular image and multimedia data, are becoming more prevalent with changing technology. Depending on the specific content of the data, image data may be considered either spatial, e.g. photographs, animation, movies, etc., or attribute, e.g. sound, descriptions, narration's, etc.

Spatial data types: It describes the absolute and relative location of geographic features. Location information is provided in maps by using points, lines and polygons. These geometric descriptions are the basic data elements of a map. Basic data elements of a map are

·        Points: They are represented as a single DOT on the map. Points are used to indicate discrete locations. They have no length or area at the given scale and usually have a single X Y coordinates. It is used to represent a feature that is too small to be displayed as a line or area.

·        Arcs: Arcs are ordered sets of Points of a straight line or a curved arc. They have a length but no width. They are accompanied by a set of coordinates. They are used to represent a geographical features that is too narrow to have area such as stream or road

·        Polygons: They have an area that is given by the arc/lines that make the boundary. They are used to represent features that have area such as lakes, large cities and islands.

GIS data models:  A GIS is based on data, hence data models are

Spatial data model: Spatial data has been stored and presented in the form of a map. Three basic types of spatial data models for storing geographic data digitally are Raster, vector and Image.

Raster data formats: Raster data set is a regular grid of cells divided into rows and columns. In a raster data set,  data values for a given parameter are stored in each cell- these values may represent an elevation in meters above sea levels, a land use class , a plant biomass in grams per square meter.

A raster data structure is in fact a matrix where any coordinate can be quickly calculated if the origin point is known and the size of the grid cell is known.

Data layer e.g. forest inventory stands, may be broken down into a series of raster maps, each representing an attribute type such as species map, a height map, density etc. referred to as one attribute maps. This is in contrast most conventional vector data models that maintain data as multiple attributed maps.

Each cell in the raster is assigning a single data value. In the example simple binary values have been used meaning that the possibilities are limited to two digit number either 0 or 1.In an 8-bit data file, there are 256 possibilities of data values for each pixel. In the example, computer sees the cells that contain 0 as turned off while the cell that contains 1 as turned on.

Advantages of Raster Data

       I.     The geographic location of each cell is implied by its position in the cell matrix.

     II.          Due to the nature of the data storage technique data analysis is usually easy to program and quick to perform.

   III.          The inherent nature of raster maps e.g. one attribute maps is ideally suited for mathematical modeling and quantitative analysis.

  IV.          Discrete data e.g. forestry stands is accommodates equally well as continuous data e.g. elevation data facilities the integrating the two data types.

Disadvantages of Raster data

1.      The cell size determines the resolution at which the data is represented.

2.      It is especially difficult to adequately  represent linear features depending on the cell resolution

3.      Processing of associated attribute data may be cumbersome if large amounts of data exist.

4.      Most input data is in vector form, data must undergo vector-to-raster conversion.

Vector data models: The fundamental vector model is a point. The various objects are created by connecting the points with straight lines but some system allows the points to be connected using arcs of circle. The term polygon is synonymous with area in vector database because of the set of straight line connections between points.

The two commonly used in GIS data storage. The topologic data structure is often referred to as an intelligent data structure because spatial relationships between geographic features are easily derived when using them.

The secondary vector data structure that is common among GIS software is the computer aided drafting (CAD) data structure. This structure consists of listing elements defined by string of vertices to define geographic features e.g. points, lines or areas.

Advantages of vector data

1.      Data can be represented at its original resolution without generalization

2.      Graphics output is usually more aesthetically pleasing.

3.      Most data e.g. hardcopy maps are vector form, no conversion us required.

4.      Accurate geographic location of data is maintained

5.      Allows for efficient encoding of topology and as a result more efficient operation that required topologic information e.g. Proximity , network analysis

Disadvantages of vector data

1.      The location of each vertex needs to be stored explicitly

2.      Algorithm for manipulative and analysis functions are complex and may be processing intensive.

3.      Continuous data such as elevation data is not effective represented in vector form

4.      Spatial analysis and filtering within polygons is impossible.

Image data format: Image data is most used to represent graphics or pictorial data. Image data is used to store remotely sensed imaginary e.g. satellite scene or ancillary graphic such as photographs, scanned plan documents etc. Image data is typically used in GIS systems as background display data or as a graphic attribute. Thus data must be converted into a raster format to be used analytically with the GIS.

Graphic image formats such as TIFF, GIF; PCX etc are used to store ancillary image data.

Attribute Data Models:  A separate data model is used to store and maintain attribute data for GIS software. These data models may exists internally within the GIS software or may be reflected in external commercial database management system (DBMS). The most common are hierarchical model, network model, relational model, object oriented model etc.

Data sources: Two types of data into a GIS, spatial and attribute. The data input process is the operation of encoding both types of data into GIS data base formats. The most common sources for spatial data are

o   Analogue maps

o   Imageries

o   Statistical data

o   Existing digital data files

Existing hard copy maps (analogue maps) provide the most popular source for any GIS project.  Because of the large cost associated with data capture and input, government departments are often the only agencies with financial resources and manpower funding to invest in data compilation.

Data input techniques:  Four basic inputting spatial data into a GIS. These are

1.      Manual digitizing

2.      Automatic Scanning

3.      Entry of coordinates using coordinates geometry

4.      Conversion of existing digital data.

·        Digitizing: A digitizer is an electronic device consisting of a table upon which the map or drawing is placed.

·        Automatic scanning:  Scanning devices exists for the automatic capture of spatial data while several different technical approaches exist in scanning technology. The advantages of automatic scanning s to capture spatial features from a map at a rapid rate of speed. Scanners are expensive to acquire and operate. As well most scanning devices have limitations with respect to the capture of selected feature e.g. text, symbol recognition.

·        Coordinate Geometry: It involves the calculation and entry of coordinates using coordinates geometry (COGO) procedure. This involves entering data from survey, explicit measurement of features from known monument. This method is useful for creating cartographic definitions of property, land records management at the cadastral or municipal scale.

·        Conversion of existing digital data:   A fourth technique that is becoming increasingly popular for data is the conversion of existing digital data. The most common digital data to be used in a GIS is data from CAD system, a number of data conversion programs exists mostly from GIS software vendors to transform data from CAD format to a raster or topological GIS data format. Some of the data formats common to the GIS marketplace are IGDS (Interactive Graphics Design Software), DLG (Digital Line Graph), DXF (Drawing Exchange Format) etc.

Data editing: It is response to the errors that arise during the encoding of spatial and non-spatial data. Editing of spatial data is time-consuming, interactive process.

They can be classified as

       I.          Incompleteness:-Includes missing point, line segments or arcs and polygons.

     II.          Location Placement Errors: Errors includes careless digitizing or poor quality of the original data source.

   III.          Distortion: Caused by base map those are not scale-correct over the whole image e.g. aerial photographs.

  IV.          Incorrect Linkages: Error due to incorrect unique identifier being assigned during manual key or digitizing.

    V.          Wrong or Incomplete Attribute: Often attribute data does not match exactly with the spatial data. This is because they are frequently from independent source, often different time periods, missing data records or too many data records in cost common problems.

Spatial Data errors: A variety of common data problems occur in converting data into a topological structure. Usually data is input by digitizing. Digitizing allows user to trace spatial data from a hard copy product e.g. a map have  to recorded by the computer software, Most GIS software has utilities to clean the data and build a topologic structure.

Attribute data Errors: The identification of attribute data errors is usually not as simple as spatial error. This is especially true if these errors are attributed to the quality or reliability of the data. Solution to these type of problem are much more complex and often do not exit entirely.

Data verification:  Data verification steps occur after data input stage and before or during the linkage of the spatial data to the attributes. Data verification ensures the integrity between the spatial and attributes data. Six steps

1.      Visual review: usually by check plotting.

2.      Cleanup of lines and junctions: Usually done by software first and interactive editing second.

3.      Weeding of excess coordinates: Involves removal of redundant vertices by the software for linear, polygonal features.

4.      Correction for Distortion and warping: GIS software has function for scale correction and rubber sheeting. The distinct rubber sheet algorithm used will vary depending on the spatial data model, vector or raster, employed by GIS.

5.      Construction of polygons: Majority of data used in GIS is polygonal, construction of polygon features from lines/arcs is necessary. This is done in conjunction with topologies building process.

6.      The addition of Unique Identifier or labels: This process is manual. Some systems do provide the capability to automatically build labels for a data layer.

Data storage and Analysis : This subsystem organizes the data both spatial and attribute in the form which permits it to be quickly retrieved for updating, querying and analysis, Most GIS software utilize software for their spatial editing and retrieval system abs database management system (DBMS) for their attribute storage.

v  Organizing data for analysis: Most GIS software organizes spatial data in a thematic approach that categorizes data in vertical layers. The definition of layers is fully dependent on the organization's requirements. Typical layers used in natural resource management agencies or companies include forest cover, soil classification, elevation, road network (access), ecological areas, hydrology etc. Spatial data layers are commonly input one at a time, e.g. Forest cover. Attribute data is entered one layer at a time.

v  Editing and updating data: The primary function in the data storage and retrieval subsystem involves the editing and updating of data. Following data editing capabilities are required

·        Interactive editing of spatial data.

·        Interactive editing of attribute data.

·        The ability to add, manipulates, modify and delete with spatial features and attributes.

·        Ability to edit selected features in a batch processing mode.

v  Data retrieval and querying:  The ability to retrieve data is based on the unique structure of the DBMS and command interfaces care commonly provided with the software. Querying is the capability to retrieve data, usually a data subset based on some user defined formula. These data subsets are often referred to as logical views. Many GIS software have attempted to standardize their querying capabilities by use of Structure Query language. This approach provides the user with the flexibility to select their own DBMS. This has direct implications if the organization has an existing DBMS that is being used for to satisfy other business requirements. It is desirable for the same DBMS to be utilized in the GIS application. The integrating of GIS software to utilize an existing DBMS through standards is referred as corporate or enterprise GIS. The use of an external DBMS linked via SQL interface is becoming the norm.  SQL is quickly becoming standard in the GIS software .

Data analysis: Geographical analysis reveals new or previously unidentified relationships within and between data sets to help to understand the real world. Geographical analysis module usually contains four important functions:

ü  Selection is important because all subsequent work is based on the result of the selection process.

ü  Manipulation has to do with aggregation, buffering, overlaying and interpolation.

ü  Exploration is the first step in discovering any kind of pattern or cluster in a data set. Explorative spatial data analysis (ESDA) uses the data in an inductive way to get new insight about spatial patterns and relations.

ü  Confirmation can be seen as tools for estimation of process models, simulation and forecasting.

 Types of GIS analysis:

       I.          Spatial measurements: Spatial measurements can be distance between two points, area of a polygons or the length of a line or boundary. Calculations can be of a simple, such as measuring areas on one map or complex such as measuring overlapping area on two or more maps.

     II.          Information Retrieval: With a GIS we can point a location, objects or area on the screen and retrieve recorded information about it from the Database management System (DBMS) which holds the information about the map's features.

   III.          Searches by attributes: Most GIS systems are simply built on the existing capabilities of a database system. Searches by attribute are thus controlled by the capabilities of database manager. Attribute queries helps to assist in our geographical searching needs.

  IV.          Searches by Geography: The GIS spatial retrieval is the generating maps, which allows searching for information visually and highlight the result.

    V.          The query interface: The user must interact with data in appropriate way, to do that we need the query interface. GIS query is usually by command line, batch or macro. Macros are files containing commands to be executed, one at a time.

  VI.          Spatial Overlay: Spatial overlay is accomplished by joining and viewing together separate data sets that share all or part of the same area. The result of this combination is a new data set that identifies the spatial relationships.

VII.          Boundary analysis: It helps to define regions according to certain criteria.

VIII.          Buffer analysis: The process involves generating a buffer around existing geographic features and identify or selecting based on whether they fail inside outside the boundary of the buffer. 

  IX.          Neighborhood operations: It can evaluate the characteristic of the area surrounding a specific location. It includes searching average, diversity, majority, maximum/minimum and total

Data output and Display:  This subsystem allows the user to generate displays, normally maps and tabular reports.

v   Graphics Display: Graphics display is the primary output mechanism of GIS. Graphics products are displayed on a video display terminal. Some other use graphics primitives such as Graphics Kernel System (GKS) to provide a more flexible interface to graphics hardware. Graphics display can be also generates for plotting on a hardcopy device.

v  Tabular Reports: The second type of output that commonly required by GIS users is the tabular or database report. Tabular reports are database listing of the result of GIS analysis matching the graphic display.

Map Projection: It is a systematic transformation of the latitudes and longitudes of location on the surface of a sphere or an ellipsoid into locations on a plane. Map projections are necessary for creating map. Map projection is a mathematical expression that is used to represent the round, 3D surface of the earth on a flat, 2D map.

Many properties can be measured on the Earth's surface independent of its geography. Some of these properties are: Area, Shape, Direction, bearing, Distance and scale. The creation of a map projection involves two steps:

1.      Selection of a model for the shape of the Earth or planetary body usually choosing between a sphere and ellipsoid. Because the Earth's actual shape is irregular, information is lost in this step.

2.      Transformation of geographical coordinates to Cartesian(x,y) or polar plane coordinated.

Remote sensing application:

Some of the major areas of remote sensing application are describes as

v  Agriculture : Satellite and airborne images are used as mapping tools to classify crops, examine their health and viability and monitor farming practices, crop type classification, crop condition assessment, crop yield estimation, mapping of soil characteristics, mapping of soil management practices, compliance monitoring etc.

v  Forestry: It includes forest cover updating, depletion monitoring and measuring biophysical properties of forest stands, forest cover type discrimination, agro forestry mapping etc.

v  Hydrology: Hydrological application include wetlands mapping and monitoring, soil moisture estimation, measuring snow thickness, determining snow water  equivalent, flood mapping and monitoring, glacier dynamics monitoring, river water /delta change detection, irrigation canal l3eakagedetection, irrigation scheduling etc.

v  Land cover and Land use : It includes natural resource management wildlife habitat protection, routing and logistics planning for seismic / exploration resource extraction activities, target detection-identification of landing strips, roads, clearing, bridges, land /water interface, legal boundaries for tax and property evolution, damage delineation etc.

v  Geology:  Remote sensing is used as a tool to extract information about the land surface structure, composition or subsurface but it often combined with other data sources providing complementary measurements.