Intro to Digital Mapping

Geographic Information Systems

Connects spatial data and list data to answer geographical questions and solve geographical problems

Spatial Data

Coordinate system

4 common spatial relationships

Distance, intersection, adjacency, containment

Common uses of GIS

Visualization, spatial modeling, social science and policy, planning and infrastructure, natural sciences, information technology

Discrete

Has clear boundaries

Examples of discrete

States, cities, countries, bodies of water

Continuous

Has no clear boundaries (except the edge of the data)

Data Model

How we encode a geographic phenomenon, be it discrete or continuous into a digital data on a computer

Vector

Points, lines or polygons defined by x, y coordinates (lat/longs) and an attribute table

Discrete

Vector data tends to be stored as

Example of vector

Political boundaries, building sites, roads, train lines

Raster

A grid of cells with values

Continuous

Raster data tends to be stored as

Example of raster

Satellite/aerial imagery, elevation

Geographic knowledges

More fundamental than maps, GIS, or even writing

Developmental and cognitive psychology

Humans have the (apparently unique) ability to think about geography abstractly

Cultural social processes

1. How people understand geography varies across different places and times


1. There are multiple kinds of legitimate geographic knowledge

Map

* A graphic representation of the environment
* A geographical proposition/argument
* Visual, abstract, geographic practice

Reference map

Involve multiple topics or themes and no one theme is most prominent

Thematic maps

* Focus on one theme
* Any of a huge variety of specific themes

Icons

The shape of Texas is an example of

Latitude

Parallel lines also known as y

Longitude

Meridian lines also known as x

Sexagesimal system

Of or related to 60

Degrees, minutes, seconds

N 40° 46’ 7”, W 73° 58’ 11”

Converting DMS to DD

A) Degrees become the whole number

B) Calculate the total number of seconds (minutes \* 60 + seconds)

C) Divide by the possible number of seconds (# from B/3600)

D) Add to the whole number

Converting DD to DMS

A) Degrees become the whole number

B) Multiply the decimal by 60 (decimal \* 60)

C) Multiply the remaining decimals by 60

Negative

Are South and West negative or positive?

Positive

Are North and East negative or positive?

Global Navigation Satellite Systems

* Space-based global navigation system that in which a receiver unit calculates its location and time
* Satellites emit radio signals. A receiver takes the signals from multiple satellites to calculate the receiver’s location

GPS receiver unit

The device that gathers GPS satellite signals and uses them to calculate your location

Fix

An accurately defined location identified with a GPS unit

Waypoint

A recorded GPS fix that is part of a series

24 satellites

Global navigation systems require at least _________ for full world-wide coverage.

Space, control and user segment

Name the 3 GPS parts

How GPS works

1. Satellites broadcast **current time** and **location**. They are **synchronized**
2. GPS receiver gets the signal and records the **time delay** between when the signal was sent vs the time the receiver got the message; indicating the **time**


1. Uses **space trilateration** to calculate its location on time delays

Space trilateration

A method for determining positions using the geometry of sphere in 3 dimensions

4

Trilateriation uses known locations of at least ___ GPS satellites

Reasons for errors in GPS

* GPS are weak
* GPS chips break
* If you drop your phone or have an old one
* Relativity
* Clock bias
* Number of visible satellites
* Dilution of precision

Systematic bias

Can anticipate this and reduce it

Random bias

Impossible to eliminate

GPS Augmentation

Using external information to improve the accuracy of GPS readings

Differential GPS

* Can be as good as 1 to 5 meters
* Uses two GPS receivers
* One at a base station
* A second moving about in a field

Spatial phenomena

* Continuous geographic phenomena
* Discrete geographic phenomena
* Stored digitally in raster and vector datasets

Non-spatial phenomena

* Categories of data measurement
* Nominal
* Ordinal
* Interval
* Ratio
* Stored digitally in attribute data

Nominal

Named types

Ordinal

Hierarchy of types

Interval

Measured difference between types based on an arbitrary zero point

Ratio

Measured difference between types based on an absolute, known zero point

Raster data

* Only one corner of the grid has a latitude and longitude (the origin: usually the upper left)
* Cells are regularly sized with no gaps
* Latitude and longitude is not stored for each cell

Resolution

The geographic size of a cell on the ground

Node

Beginning points and ending points

* Lines: beginning and ending are different
* Polygons: beginning and ending are the same

Vertex

Connecting points in the middle

Arc/segment

Line connecting points

Triangular irregular network

* X, y, z values
* Network of points defining triangles
* Best for continuous data

ESRI

Originally Environmental Systems Research Institute, replaced by ArcMap

Feature class

A single set of GIS data is called this. Appears as layers in the contents of Arc GIS.

Simple

Raster data storage is

Complex

Vector data storage is

Shapefile

Stores 1 feature class

Geodatabase

Can store multiple feature classes and other stuff