Key Concepts in Geographic Information Systems (GIS)

Six key elements of GIS

People, software, data, procedures, hardware, and network.

Three main approaches to GIS

1) GIS as a tool, 2) GIS as a developer tool, 3) GIS as a science.

Three types of location used in spatial analysis

Nominal, absolute, and relative location.

Georeferencing

Aligning spatial data to known coordinates to match real-world locations.

Spatial resolution

The level of detail in a raster dataset, determined by the size of each grid cell.

Metadata in GIS

Information about spatial data, such as source, accuracy, date, and projection.

Topological rules in GIS

Rules that define spatial relationships between features, such as connectivity and adjacency.

Spatial scale

The level of detail at which geographic phenomena are analyzed (local, regional, global).

Spatial dependence

The principle that geographic features near each other are more likely to be related than distant ones.

Spatial interpolation

Estimating values at unsampled locations based on nearby known values.

Vector data types in GIS

Point, line, and polygon.

When is raster data preferred over vector data?

When representing continuous data such as elevation, temperature, or satellite imagery.

Five principles of good map design

Legibility, visual contrast, figure-ground organization, hierarchical organization, balance.

Purpose of a map projection

To transform the 3D Earth surface onto a 2D map, minimizing distortions in area, shape, or distance.

Why does Web Mercator projection distort area near the poles?

Because it expands high-latitude regions disproportionately.

Sources of spatial inaccuracy in GIS

Satellite geometry, multipath errors, ionospheric noise, and digitization errors.

Survey123

A GIS tool for collecting geospatial data through mobile surveys.

Advantages of Survey123

User-friendly, mobile-compatible, enables real-time data collection.

Disadvantages of Survey123

Can produce inconsistent data quality, may have limited spatial accuracy, relies on internet connectivity.

PDOP (Positional Dilution of Precision)

A measure of GPS accuracy; lower values indicate better precision.

Choropleth map

A thematic map using different shades or colors to represent statistical values across geographic areas.

Modifiable areal unit problem (MAUP)

A statistical issue where spatial analysis results change depending on the scale or boundaries used.

Spatial autocorrelation

The degree to which a spatial phenomenon is correlated with itself over space.

Difference between large-scale and small-scale maps

Large-scale maps show more detail (small area), while small-scale maps show less detail (large area).

Role of attribute data in GIS

Describes characteristics of spatial features (e.g., population in a city polygon).

Primary difference between GPS and GIS

GPS determines location using satellites, while GIS analyzes spatial data relationships.

True or False: A raster is made of equal-size cells.

True.

True or False: Longitude and latitude coordinates do not depend on the datum used.

False. The datum affects the coordinate system and accuracy.

True or False: Large-scale maps show a larger portion of the Earth's surface.

False. Large-scale maps show more detail, not a larger area.

True or False: Map projections help transition from 3D to 2D but introduce distortions.

True.

True or False: Uncertainty in conception of geographic phenomena can include uncertainty in defining its boundaries.

True.

What is nominal location?

A descriptive, name-based location without precise coordinates (e.g., "New York City").

What is absolute location?

A fixed position on Earth using coordinates (e.g., latitude and longitude).

What is relative location?

A location described in relation to other locations (e.g., "5 miles west of NYC").

What is georeferencing?

Aligning spatial data to known coordinates to match real-world locations.

What is spatial resolution?

The level of detail in a raster dataset, determined by the size of each grid cell.

What is metadata in GIS?

Information about spatial data, such as source, accuracy, date, and projection.

What are topological rules in GIS?

Rules that define spatial relationships between features, such as connectivity and adjacency.

What are the three components of a GNSS (Global Navigation Satellite System)?

1) Space segment (satellites), 2) Control segment (ground stations), 3) User segment (receivers).

What is positional uncertainty?

The difference between a measured location and its true position.

What is satellite geometry?

The arrangement of satellites in the sky, which affects GPS accuracy.

What is dilution of precision (DOP)?

A measure of how satellite geometry impacts positioning accuracy; lower DOP = better accuracy.

What is ionospheric noise?

Errors caused by the ionosphere affecting satellite signals, reducing GPS accuracy.

What is multipath error?

A GPS signal bouncing off objects (e.g., buildings, trees) before reaching the receiver, leading to inaccurate readings.

What is selective availability?

Intentional GPS signal degradation used for security reasons (mostly discontinued).

What is range uncertainty?

Errors in GPS position caused by delays in satellite signals.

What is PDOP (Positional Dilution of Precision)?

A measure of satellite geometry's effect on GPS accuracy; lower PDOP is better.

What is differential positioning/correction?

A method that uses a known base station to improve GPS accuracy.

What is the difference between real-time and post-processing differential correction?

Real-time correction applies adjustments instantly, while post-processing applies corrections after data collection.

What is Wide Area Augmentation System (WAAS)?

A system that improves GPS accuracy by using ground reference stations and satellites.

What is spatial scale?

The level of geographic detail in analysis (local, regional, global).

What are the different definitions of scale in GIS?

1) Map scale (e.g., 1:50,000), 2) Spatial extent (local, regional, global), 3) Measurement scale (nominal, ordinal, interval, ratio).

What is the difference between large-scale and small-scale maps?

Large-scale maps show more detail (small area), while small-scale maps show less detail (large area).

What is spatial dependence?

The principle that geographic features near each other are more likely to be related than distant ones.

What is spatial interpolation?

Estimating values at unsampled locations based on nearby known values.

What are the five principles of good map design?

Legibility, visual contrast, figure-ground organization, hierarchical organization, balance.

What is legibility in map design?

The clarity of labels, symbols, and features to ensure readability.

What is visual contrast in map design?

relates how map features and page elements contrast with each other and their background. The higher the contrast between features, the more some features will stand out

What is figure-ground organization in map design?

the spontaneous separation of the figure in the foreground from an amorphous background. help map readers focus on a specific area of the map: adding detail to the map or using a whitewash, a drop shadow, or feathering

What is hierarchical organization in map design?

meaningful visual separation of a map into layers of

information. can convey likenesses, differences, and interrelationships

What is balance in map design?

the organization of the map and other elements on the page. results from two primary factors: visual weight and visual direction

What is the difference between primary and secondary data?

Primary data is collected firsthand (e.g., field surveys), while secondary data is obtained from existing sources (e.g., census reports).

What are common GIS file formats?

1) .csv (Comma-Separated Values) - for tabular data, 2) .shp (Shapefile) - for vector spatial data, 3) .zip - compressed GIS datasets.

How does data quality relate to validity and reliability?

Validity ensures data represents the real-world feature correctly, while reliability ensures consistent, repeatable measurements.

What is the appropriateness of data in relation to temporal, spatial, and scale attributes?

Data should be relevant in terms of time (recent enough), space (correct geographic extent), and scale (suitable level of detail).

What is a raster dataset?

A spatial dataset made up of grid cells (pixels), commonly used for continuous data like elevation or temperature.

What is a vector dataset?

A spatial dataset using points, lines, or polygons to represent discrete features like roads or city boundaries.

What are the advantages of raster data?

Best for continuous data, efficient for spatial analysis, allows mathematical operations like map algebra.

What are the disadvantages of raster data?

Large file sizes, pixelation when zoomed in, difficulty in overlaying different resolutions.

What are the advantages of vector data?

Precise, smaller file sizes, supports topology (spatial relationships).

What are the disadvantages of vector data?

Computationally complex for certain analyses, less effective for continuous data.

What are the four measurement scales?

1) *Nominal: Categories with no order (e.g., land use types). 2) Ordinal: Ranked categories (e.g., low, medium, high risk). 3) Interval: Numeric values with no true zero (e.g., temperature in Celsius). 4) Ratio:* Numeric values with a true zero (e.g., population size).

What is a conformal projection?

A map projection that preserves shape but distorts area (e.g., Mercator projection).

What is the modifiable areal unit problem (MAUP)?

A statistical issue where spatial analysis results change depending on the scale or boundaries used.

What is spatial autocorrelation?

The degree to which a spatial phenomenon is correlated with itself over space.

What is the role of attribute data in GIS?

Describes characteristics of spatial features (e.g., population in a city polygon).

What is the primary difference between GPS and GIS?

GPS determines location using satellites, while GIS analyzes spatial data relationships.