University of Pittsburgh GIS Exam

What is a GIS?

The person, the data, the computer.

Lets us visualize, question, analyze, and interpret data to understand relationships, patterns, and trends.

3 functions of GIS

input, manipulation, output

input

import data from multiple sources (like spreadsheets, satellite imagery, etc)

manipulation

view data in different visual display methods (combine maps, add distance indicators, add symbology..)

output

lay your data over an already existing map

3 applications of GIS

analysis, inventory, management (AIM)

inventory

keep track of property boundaries

analysis

use data to perform scientific experiments

management

track/monitor pollutant runoff, natural disasters

advantages of GIS over printed maps

instantly compare data sets, collaboration and crowd-sourcing, level of detail, easily reproducible, data is more flexible for different applications

advantages of printed maps over GIS

easier access in the field, no electricity or signal needed, easily annotate with your own notes/edits, portable

founders of GIS

John Snow, Ian McHarg, Roger Tomlinson

John Snow

spatially represented cholera cases on a city plan

Ian McHarg

1950's Penn st: color-coded representations of data on a map - spatial analysis represented visually.

basically, he invented layers.

Roger Tomlinson

mapped Canadian land use, coined the term GIS

ESRI

Environmental System Research Institute

ARC/INFO

first standardized ESRI software, presented data in code

types of GIS data

spatial, attribute

spatial data

geometric properties (position, length, area) of data

represented by vector OR raster

attribute data

tabular spreadsheet data, describes objects' characteristics

vector

points, lines, polygons

good for land use tracking or anything involving geopolitical boundaries

raster

grid of equal-sized cells, each designated a color to visually show variable geographic attributes,

remote sensing

how vector is plotted

(x, y)

more spatially precise: vector or raster?

vector

feature class

how vector data is packaged to be understood by the computer - collections of similar features that are all the same type of geometric representations

in an attribute table, columns are the...

attributes

in an attribute table, rows are the...

features

ways feature classes can be stored

shapefiles, inside a geodatabase

pros and cons of shapefiles

pros: compatible with older versions, small file size means fast performance

cons: made of multiple files, so they're difficult to move around

pros and cons of geodatabase feature classes

pros: easy access to all relevant data, more specific classifications of data, generally more intuitive

cons: increased size impedes performance

Geodatabase

container for attribute tables, feature classes, rasters, etc

map document

-container for and visualizer of layers, but does not contain the raw data itself.

-one layer is one version of your source data, and does not necessarily reference an entire data set (user chooses what is displayed)

-accessible from windows explorer (like a word doc)

types of GIS queries

attribute, location

editing

altering spatial or attribute data permanently

NOT changing symbology or how a feature class is represented

map layer and data source

a map layer is not a source of data, but it provides a path back to the source

GPS

global positioning system

Navstar GPS

US Department of Defense developed

LA Air Force operated

1993-1995

GNSS

Global Navigation Satellite System - includes all nationalities' GPS systems

GPS purpose

direct weapons, unified navigation for the navy

GPS use

civilian access allowed with selective ability until Clinton shut it down

selective availability

government allowed access to less accurate, degraded signal

Wide Area Augmentation System (WAAS)

ground-based receivers detect satellite positioning variations, which are then relayed to geosynchronous satellites so that data can be corrected

WAAS purpose

increase accuracy in air traffic control

Continuously Operating Reference Stations (CORS)

privately-maintained ground stations, data processed by National Geodetic Survey and NOAA. similar to WAAS

GPS constellation

6 orbital planes, 4 satellites per plane, 31 operational satellites

GPS constellation orbit altitude

median ~20,000 km

GPS constellation Air Force goal

have 24 GPS satellites online 95% of the time

how GPS determines your position

satellites constantly sending signals, receiver calculates time since signal left satellites, then triangulates based on at least 3 satellite signals

sources of GPS error

general relativity, spatial relativity, atmosphere, receiver error, satellite malfunctions, multipath error, Positional Dilution of Precision

general relativity

satellite moving much faster than the receiver - satellite has a slower clock

spatial relativity

gravity's effect on signal transmission - satellite has a faster clock

multipath error

signal bounces off ground to antennae, adds extra time

atmospheric error

ionosphere, troposphere have different indexes of refraction

positional dilution of precision

satellites close to each other have larger area of uncertainty and a greater PDOP, satellites well spaced from each other have a smaller area of uncertainty and a smaller PDOP

correcting for GPS error

receivers have almanac and ephemeris

almanac

general information on the GPS constellation

ephemeris

data about satellite path deviations

# of satellites to find 3d position

4 (3 to triangulate in 2 dimensions)

horizonal positioning is ______ accurate than vertical positioning

more

Geodesy

measure Earth's shape, orientation, gravity field

oblate ellipsoid

Earth's shape

semi-major axis (towards equator) longer than semi-minor axis (towards pole)

flattening

the effect on the planet due to its rotation that causes it to be an ellipsoid

pseudorange

calculated distance to receiver - range of space on the ground where the receiver might be

Labeling vs. Annotation

Labeling rules apply to entire layer, cannot alter individual labels.

Annotation can be added, moved, and changed individually.

Classification Methods

Manual, Equal Interval, Defined Interval, Quantile, Natural Breaks (Jenks)

Quantitative Symbology in ArcMap

Graduated Color, Graduated Symbol, Proportional Symbol, Dot Density

Symbology

The process of assigning colors, sizes, icons, widths, transparency, patterns, and other visual properties to map features in order to convey information

Public Domain

Find out when it was published (if before 1923 it is public domain)

Use without infringement of copyright law

Education, Fair Use- best known exception (commentary and criticism), Permission- if the copyright owner gives permission

Copyright Infringement

Occurs when anyone besides the copyright owner exercises rights of copyright owner

Rights of Copyright owner

Reproduction of the work, Distribution of the work, Making of derivative, public performances, public displays

When are you automatically protected under copyright law?

As soon as you create an original and protected work. Copyright registration not necessary but provides legal benefits

What is protected under copyright law?

Fixed works such as literary, musical, theatrical, graphic, dramatic.

Not the ideas or facts behind them, not scientific/historical facts

Copyright Law

A compromise between society's competing interests- to protect the creative products of its citizenry, and enable others to benefit from those products

datum

reference coordinate systems and network of surveyed points for a country or region. takes ellipsoid into account

Projections

transformation of lat/long data onto a flat surface

types of projections

planar (secant, tangent), cylindrical, conical

UTM equator: northern and southern hemisphere

0m, 10,000,000m (no negative values)

projection distortions

direction, area, distance, shape (DADS)

Universal Transverse Mercator

transverse Mercator projection + meter-based coordinate system

60.6 degree vertical swaths, UTM line goes through swath

global datum

WGS84, point of origin, Earth's center of mass

state-plane coordinate system

mapping standards for 50 states and territories

used for legal purposes

uses Lambert Conformal Conic projection

U.S. datum

NAD83, point of origin Meades Ranch, KS

cartesian

for flat maps/projections, calculating distance/surveying

(Eastings, Northings)

coordinate systems

lat/long, cartesian, datum, state-plane, universal transverse mercator

Latitude/longitude

latitude 0 +/- 90 degrees

longitude 0 +/- 180

Geoid

-measure of sea level/water table across the globe without tides, waves, etc.

-gravitational equipotential surface (GES)

Ways to select features

Interactive (using mouse), by attribute, and by location

What must there be to join tables?

Attribute table and an external table (excel)

What types of joining of tables can there be? What type can't there be?

One to one and many to one.

One to many.

What are the topological relationships?

Intersect, within a distance, within, completely within, contain/completely contain, and have their centroid in

Geoprocessing

framework in which you use tools to analyze and alter data based on spatial and attribute characteristics

What are the geoprocessing operations?

Clip, Buffer, Intersect, Union, and Difference (CBIUD)

Clip

Cookie cutter

Buffer

dissolve separate blobs into one or not

Intersect

2 shapes overlap only, "and"

Union

Where shapes are, "or"

Difference

"either but not both"

Georeferencing

Polynomial shifts

Zero Order Polynomial

Shift, translation in geometry