SSCI 125 Final Exam

Geographic Information System (GIS)

A computer system that stores, analyzes, and displays geographic data

Geographic Information Science (GISc)

Field that redefined geographic concepts and their use in the context of geographic information systems

GISc also examines the impacts of GIS on individuals and society, and the influences of society on GIS

Spatial Sciences

study of spatial patterns and relationships, and environmental interactions

interdisciplinary field including disciplines like geography, cartography, and urban planning, as well as other environment-adjacent disciplines, like logistics, security, ecology, health, and archaeology

Base Maps

the foundational, reference map layer on which other data layers are overlaid in a geographic information system (GIS)

Reference Maps

a type of map that displays the location and boundaries of geographic features and political divisions for the purpose of providing a general overview of a place (like traffic maps)

Thematic Maps

a type of map designed to showcase a specific theme or subject within a geographic area—>a map that tells a story

Geoenrichment

the process of enhancing existing geographic data by adding location-based information, like demographics, lifestyle data, or consumer behavior, to it.

Representational model

simplification of reality

in spatial sciences: representational models are used to visually convey spatial information and geographic phenomena

used to understand/depict complex interactions between human activities and the social/political/physical environment

Layers

layer model is preferred representation of spatial phenomenon within GIS

stack layers to model reality

Discrete data

Independent numbers, abrupt boundaries

categorical/discontinuous data, represents objects within distinct boundaries like buildings, roads, lakes

Continuous

represents phenomena where values vary smoothly across a surface, like elevation, temperature, or rainfall

Vector Types

Points, lines, polygones

Vector/Vector Data

represents geographic features as points, lines, and polygons, defined by coordinates and associated attribute data

These geometric shapes represent discrete features like buildings, roads, and boundaries. Vector data stores information as a collection of points, lines, and polygons, each with its own unique ID and attribute data, allowing for efficient querying and analysis

Vector Data Storage

Points are stored by their coordinates and have no dimensions

Lines and polygons are built from points

Lines have a direction in the ordering of the points and ave no width

Polygons can be built from points or lines

Spatial locations are explicit in the data model

Advantages of vectors

can zoom in on the screen and see smooth edges, independent of scale

Can be scaled to any size and retain sharpness

useful for geometic images

Raster

consists of a matrix of cells (or pixels)

Organized as a grid

Each cell contains a value representing information, like temperature

Examples: imagery from satellites, digital aerial photographs, scanned maps, modeled/interpolated surfaces (like AQI)

When to use raster vs vector

Vector is best suited for discrete data, like roads or parcels, that have clear boundaries

Raster data more suitable for continuous data, like temperature or elevation, where values vary smoothly

Raster Data Storage

Location is defined by place in the array

Entire array has to be placed on geographic coordinates

Each grid has one values, even if it’s “missing”

A cell has a resolution, given the cell size in ground units

Raster Advantages

Simple data structure

Mathematical modeling is easy because all spatial entites have a simple, regular shape

Technology is cheap

Growing availability

Raster Disadvantages

Large volumes of data

Grid resolution introduces modifiable data problem

Crude raster maps look pixelated and ugly

Coordinate transformations are difficult

Mapped Area

Region of Earth being mapped

The shape of the mapped area is influential (use of projections)

Legend Design

Symbols on the left, definitions on the right

Legend symbols must be identical to map symbols

Organize symbols by types (points, lines, polygons) and themes

Linear map features need linear legend symbols

Color is only part of a map symbol

Definitions: clear, legible text | horizontally aligned with symbols

Insets

Smaller map within larger map

4 purposes of insets: for locational information, clarify congested areas, to show related topics, to show related locations (like Alaska and Hawaii in the US)

Orientation

Gives the direction of the map

Usually indicated with a north arrow OR a graticule

Simple and subtle is best

Map users expect that True North is at the top of a map

North Arrows are needed when: true north is not at the top, the map will be used for navigation, surveying, or orienteering

Scale

Ratio of Map Distance to Earth Distance (1:25,000)

Scale can be expressed: with a representative fraction, with text, with a graphic

Scale Placement

About as subtle as the data source

Purpose is to inform, not attract attention

Fine line weights

Type should be among the smallest on the map

Units/length should be considered

Don’t forget inset maps

Choropleth Maps

uses differences in shading, coloring, or the placing of symbols within predefined areas to indicate the average values of a property or quantity in those areas

Point Feature Maps

Show the frequency at which the selected geographical phenomena occur, by displaying each individual occurrence as a dot

Points can by symbolized with different sizes to denote magnitude

Proportional symbols

Proportional symbol maps use symbols—usually circles—whose size varies in proportion to a data value at a specific location. They are similar to unclassed choropleth maps in that they represent data on a continuous scale rather than grouping values into categories.

akin to unclassed choropleth maps

Continuous scale

Graduated symbols

Graduated symbol maps represent data using symbols (often circles) whose sizes vary based on classified data ranges, rather than a continuous scale like proportional symbols. The values are grouped into categories using a classification scheme (e.g., natural breaks, quantiles, equal intervals)

Dot Density Maps

Each point represents a value of more than one occurrence of the mapped phenomena

Ex: one dot could represent 1000 people

One to many dot density maps are used when phenomena may be difficult to display one at a time

Bandwidth

radius length

Pointillism

artistic technique that relies on the ability of the eye and mind of the viewer to blend the colors of the dots into a fuller range of tones

Analogous to the four-color CMYK printing process used by some color printers and large presses that place dots of cyan, magenta, yellow, and key onto a white paper

Isolines

connect values of the same magnittude acorss the entire map

Hue

Rainbow is made up of spectral hues

Pure color

Luminosity

Brightness

Measure of lightness and darkness (matched against a gray scale)

HSV

hue, saturation, value

Spatial Scale

Scale of analysis

Country, state, census divison

Quantitative data vs qualitative data

numbers vs description/observations

Categorical color scheme

uses distinct colors to represent different categories or groups of data, without implying any order or magnitude

Diverging color scheme

pairs sequential schemes based on two different hues so that they diverge from a shared light color, from the critical midpoint, toward dark colors of different hues at each extreme.

Sequential Colors

Sequential data classes are logically arranged from high to low, and this stepped sequence of categories should be represented by sequential lightness steps

Rates

x /per _

GPS

Global Positioning System

GPS=American GNSS

Global Navigation Satellite Systems (GNSS)

Network of satellites and supporting systems that provide locational data for geolocation

China GNSS

Beidou

EU GNSS

Galileo

Russia GNSS

Glonass

Geosynchronous orbits

match earth’s spin (24-hour orbits); return to the same spot in the sky every 24 hours

Geostationary orbits

equatorial geosynchronous orbits (stay in the same spot in the sky)

Space segment

• What it is: The satellites orbiting the Earth.

• Function: Constantly send out radio signals that contain timing and location data.

• In the diagram: Represented by the satellites at the top, transmitting GNSS broadcast signals downward.

Control segment

• What it is: The network of ground stations that monitor, manage, and correct the satellites.

• Includes:

  • Master Control Station: Central hub for managing the system.

  • Data Uploading Stations: Send updated information (like clock corrections) to satellites.

  • Base Stations: Monitor satellite signals and send feedback to the master station.

• Function: Ensures satellite signals are accurate and up-to-date.

• In the diagram: Ground dishes communicating both with each other and the satellites via the GNSS control channel.

User Segment

• What it is: The GNSS receivers—like those in your phone, car, or survey equipment.

• Function: Receives satellite signals and calculates precise location using trilateration.

• In the diagram: Shown as a handheld GPS receiver on the bottom right, receiving signals from multiple satellites.

Receivers

devices the receive communication from satellites

Passive, provide for one-way communication from satellite to receiver only

Receivers can communicate with various GNSS satellite systems

Trilateration

Determination of a location using a series of distance measurements to other known locations

If we do not know the location of R, we can figure it out if we know three locations (s1, s2, s3) and R’s distance to them (d1, d2, d3)

Multipath Errors

When the signal is reflected off of an object and is delayed in reaching the receiver, the timing is off

Electro-magnetic Radiation

sensors detect energy in different parts of the electromagnetic spectrum

we can divide this spectrum into bands based on how the light energy is organized and measured

Object Identification

Objects of the same type yield similar types and amounts of radiation

A particular pattern of radiation can identify objects, and is referred to as an object’s spectral signature

All objects above 0K emit radiation and can be sensed

Active Sensing

remote sensor emits energy source and detects response from object

LiDAR, RADAR, SONAR

Passive Sensing

Remote sensor collects Red, Green, Blue, NIR Spectrum

Satellite imagery (LANDSAT)

Photography

LiDAR

Always active—>measures the 3D distance between an object and the sensor (UV, visible, and NIR bands)

Radar

radio waves