GIS Representation Method (Exam 12 may, 2014)

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Questions and Answers

Which of the following is a disadvantage of raster data representation?

Lack of topology (correct)

Handles multiple attributes

Ability to represent fuzzy objects

Complex data structure

What is one of the main advantages of using vector data in GIS?

Ability to represent continuous surface data

Simple data structure

Exact geometry (correct)

Higher storage requirements

How does raster technology reduce the amount of geographic information?

By regulating pixel size (correct)

Through weeding of unnecessary features

Storing each object as individual points

Using complex algorithms

Which projection type is characterized by less average scaling error?

Universal Transverse Mercator (D) Signup and view all the answers

Which factor contributes to the local anomalies in the geoid as compared to WGS84?

Perpendicularity to gravity at locations (B) Signup and view all the answers

Which statement best describes a disadvantage of vector data representation in GIS?

Algorithmic complexity (A) Signup and view all the answers

What is a key characteristic of passive sensors in remote sensing?

Depend on external light sources (B) Signup and view all the answers

Which of the following accurately describes the representation of polygon features in raster data?

Represented based on cell size (B) Signup and view all the answers

What is the primary function of a digital photocell in mapping technology?

Producing orthophotos (D) Signup and view all the answers

Which sensor type uses an internal source of emission?

Radar (C) Signup and view all the answers

Which of the following is NOT considered a fundamental element of a map layout?

Color palette (A) Signup and view all the answers

What distinguishes a reference map from a thematic map?

Thematic maps focus on general geographic features and locations (D) Signup and view all the answers

When planning a highway route in a GIS, which factor is least likely to influence the choice of route?

Weather patterns (D) Signup and view all the answers

What is a distinguishing feature of a formal map compared to a map-like visualization?

Formal maps include a theoretical basis and scale (A) Signup and view all the answers

Which of the following elements might be crucial in a GIS planning procedure for highway construction?

Urban center population density (D) Signup and view all the answers

In producing images on pollution using radar, what is the primary advantage of using an active sensor?

It can operate without external light sources (B) Signup and view all the answers

What is the primary representation method for discrete objects in Geographic Information Systems?

Vector data (C) Signup and view all the answers

How are line features represented within vector data?

With a start node, stop node, and intermediate vertices (C) Signup and view all the answers

Which of the following best describes raster data?

It typically contains a single value per grid cell (D) Signup and view all the answers

What characteristic defines a polygon in vector data representation?

It is a closed ring where the start and stop nodes coincide (C) Signup and view all the answers

In GIS, how are attributes handled in vector data?

Each feature corresponds to a row in an attribute table (B) Signup and view all the answers

Which feature can be represented using raster data?

Elevation over a land area (C) Signup and view all the answers

What type of features is best suited for vector data representation?

Discrete natural features like rocks or trees (A) Signup and view all the answers

Which of the following statements is NOT true about raster data?

It is primarily for discrete objects. (D) Signup and view all the answers

Study Notes

GIS Representation Methods

Vector data uses x,y coordinates to represent discrete objects.
- Points: Single coordinate pair (e.g., a tree).
- Lines: Connected coordinate pairs (e.g., a road).
- Polygons: Closed rings of coordinates (e.g., a building).
- Attributes: Data associated with features in a table.
- Topology: Stores relationships between features (adjacency, containment).
Raster data uses a grid of cells to represent continuous fields.
- Cells: Contain a value representing a feature (e.g., elevation, temperature).
- Grid: Often square, defined by real-world coordinates.
- No topology: Does not store relationships between features.
- Good for continuous data: Elevation, temperature.

GIS Feature Representation

Points, lines, and polygons are fundamental GIS features.
These features can represent real-world phenomena.
- Points: Trees, poles.
- Lines: Roads, rivers.
- Polygons: Buildings, lakes.

Geo-referencing and Attributes

Geo-referencing: Locating features in real-world space. Raster by cell location, vector by coordinate pair.
Attributes: Descriptive data associated with each feature.
- Different types of data (text, number, date) stored in tables.

Raster Advantages & Disadvantages

Advantages:
- Simple structure.
- Stores continuous data (e.g., temperature).
- Represents fuzzy objects (e.g., wetlands).
Disadvantages:
- No topology.
- Large storage requirements.

Vector Advantages & Disadvantages

Advantages:
- Exact geometric representation.
- Stores multiple attributes.
- Defined topology.
Disadvantages:
- Unreasonable precision.
- Algorithmic complexity.
- Inability to represent continuous phenomena.

Fundamental GIS Problem

Reduce complex geographical data into manageable computer representations.
Raster: Controls via pixel size.
Vector: Reduces data by weeding and controlling vertices.

Geoid and Local Datums

Geoid: Surface aligning with gravity.
Local Ellipsoid: Models the geoid locally.
Differences used to create a local datums.

Secant Map Projection

Secant: Rotated cylinder to cover Earth's circumference.
Less average scaling error compared to tangential projections.

Passive vs Active Sensors

Passive: Detects reflected external emission (e.g., photos).
Active: Contains an internal emission source (e.g., radar).
Results: Orthophotos(passive), pollution measurements (active).

Ortho-correction

Improves map accuracy.
Corrects distortions introduced by the imaging process.

Map Elements

Map components for presentation include title, legend, scale, projection, data source, copyright, north arrow, and inset map.

Highway Planning Considerations

Existing roads, Urban centers, nature reserves, Hydrography, and political needs.
GIS data must encompass the required decision areas.

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Description

Explore the methods of representing geographic information systems (GIS) through vector and raster data. Understand how points, lines, and polygons represent real-world phenomena, and learn about the attributes and topology involved in GIS representation. This quiz will test your knowledge on these fundamental concepts.