1. GIS
QUESTIONS AND ANSWERS

2. 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.

3. 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.

4. 19. What is remote sensing (Modern Definition)?
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.

5. 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.

6. 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.

7. 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).

8. 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.

9. What are WMS?
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.
What are WCS?
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.

10. What are WMS WCS and WFS?
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.

11. 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.

12. 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.

13. 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.

14. 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.
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.

15. What is Intersect function?
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.
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.

16. What is Union function?
Only polygon coverages can be used by the Union tool. 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.

17. 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.

18. 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).

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

20. 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.

21. Thanks…