1. GIS
QUESTIONS AND ANSWERS

2. 1. What is projection?
A map projection is one of many methods used to represent the 3-dimensional surface of the earth or other round body on a 2-dimensional plane in cartography (mapmaking).
A Projection is a series of transformations which convert
the location of points on a curved surface (the reference surface or datum) to locations on flat plane (i.e. transforms coordinates from one coordinate reference system to another).

3. 2. What are different projection systems? Azimuthal projections
Azimuthal projections touch the earth to a plane at one tangent point; angles from that tangent point are preserved, and distances from that point are computed by a function independent of the angle. Azimuthal equidistant projection is used by amateur radio operators to know the direction to point their antennas toward a point and see the distance to it. Distance from the tangent point on the map is equal to surface distance on the earth.
Azimuthal equal-area projection: distance from the tangent point on the map is equal to straight-line distance through the earth.
Azimuthal conformal projection is the same as stereographic projection.

4. Azimuthal orthographic projection maps each point on the earth to the closest point on the plane.
Conformal projections
Conformal map projections preserve angles. Mercator projection wraps a cylinder around the earth; the distance from the equator on the map is being geographical latitude, on a scale where the earth’s radius is 1.
Stereographic projection touches a plane to the earth and projects each point in a straight line from the antipode of the tangent.
Equal-area projections
These projections preserve area.

5. Gall-Peters projection wraps a cylinder around the earth and maps each point on the earth to the nearest point on the cylinder.
Cordiform projection designates a pole and a meridian; distances from the pole are preserved, as are distances from the meridian (which is straight) along the parallels.

6. 3. What is a coordinate system?
Coordinate systems enable geographic datasets to use common locations for integration. A coordinate system is a reference system used to represent the locations of geographic features, imagery, and observations, such as Global Positioning System (GPS) locations, within a common geographic framework.
Each coordinate system is defined by the following:
Its measurement framework, which is either geographic (in which spherical coordinates are measured from the earth's center) or planimetric (in which the earth's coordinates are projected onto a two-dimensional planar surface)
Units of measurement (typically feet or meters for projected coordinate systems or decimal degrees for latitude- longitude)

7. The definition of the map projection for projected coordinate systems
Other measurement system properties such as a spheroid of reference, a datum, one or more standard parallels, a central meridian, and possible shifts in the x- and y- directions
Several hundred geographic coordinate systems and a few thousand projected coordinate systems are available for use. In addition, you can define a custom coordinate system.

8. 4. Mention Types of coordinate systems
The following are two common types of coordinate systems used in a geographic information system (GIS):
A global or spherical coordinate system such as latitude- longitude. These are often referred to as geographic coordinate systems.
A projected coordinate system such as universal transverse Mercator (UTM), Albers Equal Area, or Robinson, all of which (along with numerous other map projection models) provide various mechanisms to project maps of the earth's spherical surface onto a two-dimensional Cartesian coordinate plane. Projected coordinate systems are referred to as map projections.
Coordinate systems (both geographic and projected) provide a framework for defining real-world locations.

9. 5. What is a spatial reference?
A spatial reference is a series of parameters that define the coordinate system and other spatial properties for each dataset in the geodatabase. It is typical that all datasets for the same area (and in the same geodatabase) use a common spatial reference definition.
A spatial reference includes the following:
The coordinate system
The coordinate precision with which coordinates are stored (often referred to as the coordinate resolution)
Processing tolerances (such as the cluster tolerance)
The spatial extent covered by the dataset (often referred to as the spatial domain)

10. 6. What is Geographic coordinate systems
A geographic coordinate system (GCS) uses a three- dimensional spherical surface to define locations on the earth. A GCS is often incorrectly called a datum, but a datum is only one part of a GCS. A GCS includes an angular unit of measure, a prime meridian, and a datum (based on a spheroid). The spheroid defines the size and shape of the earth model, while the datum connects the spheroid to the earth's surface.
A point is referenced by its longitude and latitude values. Longitude and latitude are angles measured from the earth's center to a point on the earth's surface. The angles often are measured in degrees (or

11. in. grads). The. following. illustration. shows. the
in grads). The following illustration shows the world as a globe with longitude and latitude values:
In the spherical system, horizontal lines, or east–west lines, are lines of equal latitude, or parallels. Vertical lines, or north–south lines, are lines of equal longitude, or meridians. These lines encompass the globe and form a gridded network called a graticule.

12. The line of latitude midway between the poles is called the equator
The line of latitude midway between the poles is called the equator. It defines the line of zero latitude. The line of zero longitude is called the prime meridian. For most GCSs, the prime meridian is the longitude that passes through Greenwich, England. The origin of the graticule (0,0) is defined by where the equator and prime meridian intersect.
Latitude and longitude values are traditionally measured either in decimal degrees or in degrees, minutes, and seconds (DMS). Latitude values are measured relative to the equator and range from –90° at the south pole to +90° at the north pole. Longitude values are measured relative to the prime meridian. They range from –180° when traveling west to 180°

13. when traveling
east.
If the prime
meridian is at
the
Greenwich, then Australia, which is south of
equator and east of Greenwich, has positive longitude values and negative latitude values.
It may be helpful to equate longitude values with x and latitude values with y. Data defined on a geographic coordinate system is displayed as if a degree is a linear unit of measure. This method is basically the same as the Plate Carrée projection. A physical location will usually have different coordinate values in different geographic coordinate systems.

14. 7. What is Geographic (datum) transformations
If two datasets are not referenced to the same geographic coordinate system, you may need to perform a geographic (datum) transformation This is a well-defined mathematical method to convert coordinates between two geographic coordinate systems. As with the coordinate systems, there are several hundred predefined geographic transformations that you can access. It is very important to correctly use a geographic transformation if it is required. When neglected, coordinates can be in the wrong location by up to a few hundred meters. Sometimes no transformation exists, or you have to use a third GCS like the World Geodetic System (WGS84) and combine two transformations.

15. 8. What is Projected coordinate systems
A projected coordinate system (PCS) is defined on a flat, two-dimensional surface. Unlike a GCS, a PCS has constant lengths, angles, and areas across the two dimensions. A PCS is always based on a GCS that is based on a sphere or spheroid. In addition to the GCS, a PCS includes a map projection, a set of projection parameters that customize the map projection for a particular location, and a linear unit of measure.

16. 9. Compare Geographic vs. Projected Coordinates
Advantages of the spherical coordinate system—You can represent any point on the Earth’s surface as accurately as your measurement techniques allow. The system itself does not introduce errors.
Disadvantages of a spherical coordinate system—You will encounter complex and time-consuming arithmetic calculations in determining the distance
between polygon longitude
two points
or the area surrounded by a by a set of points. Latitude-
determined numbers
plotted directly on paper in a
Cartesian coordinate system result sometimes greatly distorted—figures.
in distorted—

17. Advantages of a projected coordinate system on the Cartesian plane—Calculations of distances between points are trivial. Calculations of areas are relatively easy. Graphic representations are realistic, provided the area covered is not too large.
Disadvantages of a projected coordinate system on
the Cartesian plane—Almost every point is in the wrong place, although maybe not by much. All
the
projections introduce errors. Depending on projection, these errors are in distances,
sizes,
shapes, or directions.

18. 10. What is a scale.?
The scale of a map is the ratio of a distance on the map to the corresponding distance on the ground.
Representation of scale
Map scales may be expressed in words (a lexical scale), as a ratio, or as a fraction. Examples are:
'one centimetre to one hundred metres' or 1:10,000 or 1/10,000
'one inch to one mile' or 1:63,360 or 1/63,360 'one centimetre to one thousand kilometres' or 1:100,000,000 or 1/100,000,000. (The ratio would usually be abbreviated to 1:100M

19. 11. What is geocoding?
Geocoding is a process is the process of assigning locations to addresses to that they can be placed as points on a map, similar to putting pins on a paper map, and analyzed with
other spatial coordinates to geocoding.
data. The process the original data,
assigns geographic hence the name
12. What is reverse geocoding?
Reverse geocoding is the process of back (reverse) coding
of a point location (latitude, longitude) to a readable address or place name. This permits the identification of nearby street addresses, places, and/or areal subdivisions such as neighborhoods, county, state, or country. Combined with geocoding and routing services, reverse geocoding is a critical component of mobile location-based services to convert a coordinate obtained by GPS to a readable street address which is easier to understand by the end user.

20. 13. What is geo-referencing?
Georeferencing is the process of taking a raster image or vector coverage, assigning it a coordinate system and coordinates, and translating, transforming, and warping/rubbersheeting it into position relative to some other spatial data, such as survey locations, street intersections, etc.
This can be sometimes also be called rectification or
georectification interchangeably, while in some contexts, georeferencing is considered to only include the assigning of a spatial reference and coordinates to the image, and rectification is the transformation and resampling of the image to remove distortion (as in orthorectification).

21. 14. What is geo-processing?
Geoprocessing is a GIS operation used to manipulate spatial data. A typical geoprocessing operation takes an input dataset, performs an operation on that dataset, and returns the result of the operation as an output dataset. Common geoprocessing operations include geographic feature overlay, feature selection and analysis, topology processing, raster processing, and data conversion. Geoprocessing allows for definition, management, and analysis of information used to form decisions.
15. What is BLOB?
A Binary Large OBject (BLOB) is a collection of binary data stored as a single entity in a database management system.
Blobs are typically images, audio or other multimedia objects, though sometimes binary executable code is stored as a blob. Database support for blobs is not universal.

22. 16. What is the full meaning of GPS?
The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the earth where there is an unobstructed line of sight to four or more GPS satellites.

23. 17. The role of GPS in GIS.
The uses of GIS, GPS,
and RS technologies,
either
individually or in combination, span a broad range of applications and degrees of complexity. Simple applications might involve determining the location of sampling sites, plotting maps for use in the field, or examining the distribution of soil types in relation to yields and productivity. More complex applications take advantage of the analytical capabilities of GIS and RS software. These might include vegetation classification for predicting crop yield or environmental impacts, modeling of surface water drainage patterns, or tracking animal migration patterns.
Precision Agriculture
Forest Management
Habitat Analysis
Data Analysis and Display

24. 18. What is GIS?
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. This enables people to more easily see, analyze, and understand patterns and relationships.

25. 19. What is remote sensing?
Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with
the object and Remote sensing
thus in contrast to on site observation. is used in numerous fields, including
geography and most Earth Science disciplines (for example, hydrology, ecology, oceanography, glaciology, geology); it also has military, intelligence, commercial, economic, planning, and humanitarian applications. In modern usage, the term generally refers to the use of aerial sensor technologies to detect and classify objects on Earth (both on the surface, and in the atmosphere and oceans) by means of propagated signals (e.g. electromagnetic radiation). It may be split into active remote sensing (when a signal is first emitted from aircraft or satellites) or passive (e.g. sunlight) when information is merely recorded.

26. 20. What is cartography. Cartography. is. the. study. and. practice of
20. What is cartography? Cartography is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.

27. 21. Data structures that can hold spatial data.
Spatial data are what drive a GIS. Every functionality that makes a GIS separate from another analytical environment is rooted in the spatially explicit nature of the data.
Spatial data are often referred to as layers, coverages, or layers. Layers represent, in a special digital storage format, features on, above, or below the surface of the earth. Depending on the type of features they represent, and the purpose to which the data will be applied, layers will be one of 2 major types.
Vector data represent features as discrete points, lines, and polygons.
Raster data represent the landscape as a rectangular matrix of square cells.

28. Depending on the type of problem that needs to be solved, the type of maps that need to be made, and the data source, either raster or vector, or a combination of the two can be used.
22. Open Standards related to GIS.
The Open Geospatial Consortium (OGC), an international voluntary consensus standards organization, originated in
1994. In the OGC, more than 500 governmental, nonprofit and research
commercials, organizations
worldwide collaborate in a consensus process encouraging development and implementation of open standards for geospatial content and services, GIS data processing and data sharing.
23. What is Datum?
A Geodetic datum or geodetic system is a coordinate system, and a set of reference points, used to locate places on the Earth (or similar objects).

29. 24. What are Web services?
A web service is any piece of software
that makes itself available over the internet and uses a standardized XML messaging system. XML is used to encode all communications to a web service. For example, a client invokes
a web service by message, then
sending waits
an XML for a
corresponding XML response.

30. 25. What are WMS WCS and WFS?
Web Mapping Service (WMS) – A standard protocol for serving georeferenced map images over the internet that are generated from a map server using data from a GIS database. It’s important to note that with a WMS, you are essentially getting an image of geospatial data (i.e. JPG, GIF, PNG file). While this has its uses, it is an image only, and therefore does not contain any of the underlying geospatial data that was used to create the image.
Web Coverage Service (WCS) – A standard protocol for serving coverage data which returns data with its original semantics (instead of just pictures) which may be interpreted, extrapolated,etc., and not just portrayed. Essentially,a WCS can be thought of as the raw geospatial raster data behind an image. Using a WCS, you can pull

31. the raw raster information you need to perform further analysis.
Web Feature Service (WFS) – A standard protocol for serving geographical features across the web using platform-independent calls. A WFS can be thought of as the vector geospatial data behind a map. Using a WFS, you can pull only the vector file information that you need and apply it to a wide variety of purposes, including purposes other than the producers’ intended ones.

32. 26. What is snapping?
An automatic editing operation in which points or features within a specified distance (tolerance) of other points or features are moved to match or coincide exactly with each other’s coordinates.
Snapping allows you to create features that connect
to each other so your edits are more accurate, with
fewer errors. When snapping is turned on, your
pointer will jump, or snap to, edges, vertices, and
other geometric elements when your pointer is near
them and within a certain tolerance. This enables
you to position a feature easily in relation to the
locations of other features.

33. 27. What is Overlay?
Overlay analysis is one of the spatial
GIS operations. Overlay
integrates spatial data with
analysis attribute
data. (Attributes are information about each map feature.) Overlay analysis does this by combining information from one GIS layer with another GIS layer to derive or infer an attribute for one of the layers.

34. What do you understand from Topology?
A GIS topology is a set of rules and behaviors that model how points, lines, and polygons share coincident geometry. For example: Adjacent features, such as two counties, will have a common boundary between them. They share this edge.
What is Network Analyst?
A network is a system of interconnected elements, such as edges (lines) and connecting junctions (points), that represent possible routes from one location to another.
Network Analyst provides network-based spatial analysis
tools for solving complex routing problems. It uses a configurable transportation network data model, allowing organizations to accurately represent their unique network requirements.

35. What are sliver polygons?
A small, narrow, polygon feature that appears along the borders of polygons following the overlay of two or more geographic datasets. Sliver polygons may indicate topology problems with the source polygon features, or they may be a legitimate result of the overlay.
What is the difference between a Union and an Intersect function?
Identity tool
To use the Identity tool, the input coverage can be a point, line, or polygon coverage. The output coverage will be the same feature type as the input coverage.
All features of the input coverage will be preserved in the output coverage. This means that the input coverage acts like a cookie cutter on the identity coverage.

36. The three feature types are affected differently by the identity coverage:
Polygons: Input coverage arcs are split at their intersections with polygons of the identity coverage.
Lines: Identity coverage arcs are used to split input coverages where they overlap.

37. Points: All input coverage points are saved in the output coverage, and the output coverage PAT file lists the identity coverage polygon within which each point falls.
The Intersect and Union tools are similar to the Identity tool. The only difference is the features that remain in the output coverage.
Intersect tool
To use the Intersect tool, the input coverage can be a point, line, or polygon coverage. The output coverage will be the same feature type as the input coverage.
Only those features contained by polygons in the intersect coverage will be preserved in the output coverage.

38. The Intersect tool is similar to the Clip tool; however, the Clip tool does not transfer any attributes from the clip coverage to the output. The Intersect tool is also similar to the Identity and Union tools. The only difference is the features that remain in the output coverage.
Union tool
Only polygon coverages can be used by the Union tool.

39. The output coverage contains the polygon features from both the input and union coverage. Unlike Identity and Intersect, Union never clips any data.
The Union tool is similar to the Intersect and Identity tools. The only difference is the features that remain in the output coverage.

40. 32. What is the difference between CAD and GIS?
GIS data normally covers a large geographic area, where CAD data are normally much smaller areas.
GIS data is normally displayed at smaller scales than CAD data.
GIS data is often captured with less accuracy than CAD data.
GIS data normally include attribute information, where CAD data historically haven’t.

41. What is meant by the term 'accuracy'?
What is meant by the term 'precision'?
Accuracy can be defined as the degree or closeness to which the information on a map matches the values in the real world. Therefore, when we refer to accuracy, we are talking about quality of data and about number of errors contained in a certain dataset. In GIS data, accuracy can be referred to a geographic position, but it can be referred also to attribute, or conceptual accuracy.
Precision refers how exact is the description of data. Precise data may be inaccurate, because it may be exactly described but inaccurately gathered. (Maybe the surveyor made a mistake, or the data was recorded wrongly into the database).

42. 35. Sources Data?
of Errors
in GIS
Conception
Measurement
Representation
Analysis

43. 36. What is Monte Carlo simulation?
An algorithm for computing solutions to problems that contain a large number of variables by performing iterations with different sets of random numbers until the best solution
is found. problems computer.
The Monte Carlo too complex for
method is usually applied to analysis by anything but a
Monte Carlo Simulation utilizes a sequence of algorithms that generate a number of random values. This process is useful when attempting to generate data, given some specific constraints; for example, mean and standard deviation. Monte Carlo methods can also produce random values to create a distribution if a current distribution is not known. These methods are generally used to provide test data for model simulations or other computerized calculations that require large amounts of values.

44. Thanks…