1 - Introduction to GIS

Question 1

Q: What is GIS?

Answer 1

A: GIS (Geographic Information System or Science) is a computer system for managing geographic data tied to specific locations. It allows users to map, model, store, and analyze data.
Key Functions:

Pinpoint locations.
Perform routing (e.g., in-car navigation).
Report power outages.
Analyze crime patterns.
Predict weather.

Question 2

Q: What was the first GIS system, and when was it developed?

Answer 2

A:

The first GIS system was the Canada Geographic Information System (CGIS), developed in the mid-1960s.
Other Key Milestones:
1970: U.S. Census produced its first geocoded census.
1990: TIGER database created the first nationwide digital map of roads, boundaries, and water in the U.S.
1995: UK Ordnance Survey digitized 230,000 maps to create the first large-scale electronic mapping program.

Question 3

Q: Describe Dr. John Snow’s contribution to GIS history

Answer 3

A: In 1854, Dr. John Snow mapped cholera deaths in central London, revealing a contaminated well as the outbreak’s source. This marked the birth of modern thematic mapping and disease mapping.

Question 4

Q: What percentage of all database information contains geographic elements?

Answer 4

A: Approximately 80% of all information in databases includes some geographic element (e.g., addresses, buildings, postal codes, property, or road junctions).

Question 5

Q: What are the two main GIS data models, and how are they used?

Answer 5

A:

Vector Model:
Represents discrete data using points, lines, and polygons.
Example: City names, road networks.

Raster Model:
Represents continuous data using a grid or pixels.
Example: Temperature gradients, elevation models

Question 6

Q: What are the primary components of a shapefile in GIS?

Answer 6

A: A shapefile comprises the following files:

Main File (.shp): Stores feature geometry.
Index File (.shx): Links features with the corresponding record in the attribute table.
Database File (.dbf): Stores attribute data and object IDs.
Projection File (.prj, optional): Provides coordinate reference system info.

Question 7

Q: What is the difference between discrete and continuous data in GIS?

Answer 7

A:

Discrete Data: Represents features with definite boundaries (e.g., cities, roads, wards). It’s categorical or nominal and represented as distinct values.
Continuous Data: Represents features without defined boundaries (e.g., temperature, elevation). It’s measured on a continuous scale, often visualized as gradients or heat maps.

Question 8

Q: How does GIS process geographic data?

Answer 8

A:

Captures data in digital form.
Classifies features as points (e.g., schools), lines (e.g., roads), or polygons (e.g., lakes).
Stores data in geometry (shapes and locations) and attributes (descriptive info)

Question 9

Q: What is ArcGIS Pro, and what are its capabilities?

Answer 9

A:
ArcGIS Pro is a professional desktop GIS application from Esri. It enables:

Exploring, visualizing, and analyzing data.
Creating 2D maps and 3D scenes.
Sharing work through ArcGIS Online or an organization portal.

Question 10

Q: What is a vector data model in GIS?

Answer 10

A:
The vector data model represents geographic features as points, lines, and polygons:

Points: Represent discrete locations (e.g., schools, landmarks).
Lines: Represent linear features (e.g., roads, rivers).
Polygons: Represent areas with boundaries (e.g., lakes, city boundaries).
Key Features:
Suitable for discrete data with clear boundaries.
High precision for representing location and shape.
Stored as geometries (spatial features) and attributes (descriptive information).

Question 11

Q: What is a raster data model in GIS?

Answer 11

A:
The raster data model represents geographic information as a grid of cells or pixels:

Each cell holds a value corresponding to the attribute (e.g., elevation, temperature).
Best suited for continuous data, such as gradients or surfaces.
Key Features:
Useful for modeling and analyzing continuous phenomena.
Data resolution depends on cell size; smaller cells provide greater detail.
Example applications: Satellite imagery, digital elevation models (DEM)

Question 12

Q: What are the advantages and disadvantages of vector data?

Answer 12

A:
Advantages:

High precision for representing locations and boundaries.
Compact storage; efficient for small datasets.
Easily edited and updated.
Disadvantages:

Computationally intensive for complex operations.
Less suitable for representing continuous phenomena

Question 13

Q: What are the advantages and disadvantages of raster data?

Answer 13

A:
Advantages:

Excellent for representing continuous surfaces.
Simple data structure.
Supports complex spatial analysis using mathematical operations (e.g., map algebra).
Disadvantages:

Large file sizes, especially with high-resolution data.
Lower precision for boundaries and small features

Question 14

Q: How are vector and raster data georeferenced?

Answer 14

A:
Both vector and raster data are tied to real-world coordinates using georeferencing:

Vector Data: Points, lines, and polygons are defined with latitude and longitude or projected coordinates.
Raster Data: Each cell is assigned a location based on its row and column within a defined coordinate system

Question 15

Q: What is the significance of resolution in raster data?

Answer 15

A:
Resolution refers to the size of each cell in the raster grid:

High Resolution: Smaller cells capture finer details but require more storage.
Low Resolution: Larger cells are less detailed but more efficient to process.
Example: A raster with a 1-meter resolution can represent finer details than one with a 10-meter resolution

Question 16

Q: What file formats are commonly used for vector and raster data?

Answer 16

A:

Vector Formats: Shapefile (.shp), GeoJSON, KML.

Raster Formats: GeoTIFF, JPEG, PNG, GRID.
Both formats are supported by GIS software like ArcGIS and QGIS

Question 17

Q: What is the difference between discrete and continuous data, and how do vector and raster models handle them?

Answer 17

A:

Discrete Data (Vector): Features like roads, buildings, and political boundaries, where each element is distinct. Represented as points, lines, or polygons.
Continuous Data (Raster): Phenomena like temperature, elevation, and rainfall that vary smoothly across space. Represented as cell grids with gradient values.

Question 18

Q: What is map algebra in the raster model

Answer 18

A:
Map algebra involves applying mathematical operations to raster data layers:

Operations include addition, subtraction, multiplication, and more.
Example: Combining elevation and land use layers to determine suitable locations for development.

Question 19

Q: What are the primary components of a shapefile in GIS, and what do they do?

Answer 19

A: A shapefile is a vector data format widely used in GIS, comprising several essential files that work together to store geometric and attribute information. The primary components are:

Main File (.shp):

Stores the geometric data of features (e.g., points, lines, polygons).
Defines the spatial representation of map features (e.g., city locations, road networks).
Mandatory file for all shapefiles.
Index File (.shx):

Provides a positional index to link geometries in the .shp file with corresponding attributes in the .dbf file.
Ensures fast access to features and their associated records.
Database File (.dbf):

Stores attribute data in tabular form, such as names, population, or other descriptive information.
Uses a standard database format compatible with software like Microsoft Excel or Access.
Mandatory for all shapefiles.
Projection File (.prj) [Optional]:

Contains the coordinate reference system (CRS) information, including datum, projection type, and measurement units.
Essential for aligning data correctly on a map. Without this file, the spatial data may be misaligned.
Other Auxiliary Files [Optional]:

.cpg: Specifies the character encoding for the attribute data.
.xml: Contains metadata about the shapefile, such as creation date and purpose.
.sbn/.sbx: Used for spatial indexing to improve performance in some software.
Example:
When opening a shapefile (e.g., “UK_Local_Authority”) in GIS, you’ll typically see multiple files like UK_Local_Authority.shp, UK_Local_Authority.shx, and UK_Local_Authority.dbf. Together, these files enable the storage and manipulation of spatial and non-spatial data seamlessly.

Key Fact: A shapefile is not a single file but a combination of at least three core files (.shp, .shx, .dbf) working in unison to represent vector data effectively.