BSEN 5220 - Exam 2 - Jasmeet Lamba

How is GIS different from other information systems?

Contains spatial data

Geodesy

Study of the shape and size of the earth and its gravity field

Shape of the earth

Spheroid

Geodetic Coordinate System

Allows positions on the earth's surface to be described in terms of latitude, longitude, and height

Latitude (Parallels)

East to west - 0deg at the Equator to 90deg at the poles

Longitude (Meridians)

North to south - 0deg at the Prime Meridian. Range from 0deg to 180deg

Ellipsoid

Best fit mathematical shapes to "average" out the shape of the earth
- Has a mathematical definition
- Simple geometrical surface
- Described by 2 parameters
- Cannot be used by an instrument

Geoid

The actual shape of the earth
- Physical definition
- Complicated surface
- Described by infinite number of parameters
- Can be sensed by instruments

Heights refer to the

Mathematical model (ellipsoid)

Elevations refer to

Mean sea level

Ellipsoidal height

Height above the reference ellipsoid

Orthometric height

The difference between ellipsoidal height and geoidal height at any location

One degree of longitude

At the equator - 1deg = 112.09km
At the poles - 1deg = 0km

One degree of latitude

At the equator - 1deg = 110.57km
At the poles - 1deg = 111.70km

Datum

A mathematical model of the earth, which serves as the reference or base for calculating the geographic coordinates of a location

Important components of the datum

- Specifications of an ellipsoid
- Set of points that have been surveyed and an estimate of the coordinate of each point

Earth centered

Geocentric; mass center = ellipsoid center

Datum - WGS 1984

- Area - Global
- Origin - Earth center of mass
- Ellipsoid - WGS 84

Datum - NAD 1983

- Area - North America, Caribbean
- Origin - Earth center of mass
- Ellipsoid - GRS 80

Datum - NAD 1927

- Area - North America
- Origin - Meades Ranch
- Ellipsoid - Clarke 1866

Datum - European 1950

- Area - Europe, Middle East, North Africa
- Origin - Potsdam
- Ellipsoid - International

Datum shift

A change from one datum to another, such as from NAD27 to NAD83, which can result in substantial horizontal shifts of point positions

Map projection

A systematic rendering of locations from the curved earth surface onto a flat map surface

Conformal map projection

Preserve local shape, no map projection can preserve shapes of larger regions

Equal-area map projection

Retain all areas at the same scale

Equidistance map projection

Maintain certain distance or consistency of a scale along certain lines

True-direction map projection

Express certain accurate directions

Map projection groups

- Cylindrical
- Conic
- Plane

Point of tangency

Point of contact between surface and projection

Standard line in map projection

The line of true scale (line of contact)

Conic projections

- One or two points of contact
- Distortion increases away from standard parallel

Cylindrical projections

- Mercator projection
- Conformal and displays true direction along straight lines

Planar projections

Projection of the globe onto a plane

Planar - orthographic projection

The point of perspective is at infinite distance on the opposite direction from the point tangency

Planar - gnomonic projection

The point of perspective or the light source is located at the center of the globe

Planar - stereo graphic projection

The perspective point is located on the surface of globe directly opposite from the point of tangency of the plane

Two commonly used projections

- Lambert Conformal Conic Projection
- Transverse Mercator

Locations that are E-W oriented are less distorted when using _______

Lambert Conformal Conic Projection

Locations that are N-S oriented are less distorted when using ________

Universal Transverse Mercator (cylindrical)

Universal Transverse Mercator

- X (easting) and Y (northing) coordinates
- 60 zones (6deg wide, 8deg tall)
- Zones extend from 80S to 84N

First zone of UTM starts at the ______

International Date Line

If one state is in two UTM zones, use ________

Scale based coordinate system

Central Meridian

- Each zone has its own
- Is not the same as Prime Meridian

UTM zones

- All coordinates are positive
- Equator assigned a northing value of zero for all north zones

Why use UTM projection?

- UTM provides a constant distance relationship (true-distance) anywhere on the map
- Coordinates are tied directly to distance
- No negative numbers or E-W designators
- Coordinates are decimal based
- Coordinates are measured in metric units

State Plane Coordinate System

- USA only
- 50 states and 20 zones
- Lambert Conformal and UTM used as basis
- State and county boundaries establish zones

Things to consider when choosing map projection

- Database's primary use
- Area
- Location
- Extent of the area (N-S or E-W)

Two step process to changing a projection of a map that is already stored in a real-world coordinate system

- Inverting projections
- Forward transformation

For any geo-referenced, digital map one must know the ____, ____, and ____ in order to build a GIS database

Datum; projection; units

Small map scale

Can show large areas without much detail

Large map scale

Can show a lot of detail but small areas

Map resolution

Refers to how accurately the location and shape of map features can be depicted for a given map scale

Factors influencing map accuracy

- Flattening the round earth onto a 2-D surface
- Accurately measuring location on earth
- Digitizing processor error
- Machine precision

The three ArcGIS Desktop applications

- ArcMap
- ArcCatalog
- ArcToolbox

With ArcMap you can:

- Make maps from layers of spatial data
- Choose colors and symbols
- Query attributes
- Analyze spatial relationships
- Design map layouts

ArcMap contains:

- A list (or table of contents) of the layers in the map
- A display area for viewing the map
- Menus and tools for working with the map

Data frames

Containers for a dataset

In table of contents, you can list by:

- Drawing Order
- Source
- Visibility
- Selection

ArcCatalog

- Helps you organize and manage all your GIS data
- Browsing data on hard disk, network, or internet
- Search spatial data, preview it, and add it to ArcMap
- Managing metadata
- Similar to Windows Explorer

The changes you make in files in ArcCatalog window will be ____

Permanent

ArcToolbox

- Hundreds of tools
- You can create custom toolset
- Projection change
- Data overlay
- File format conversion

ArcGIS 3D Analyst

Three-dimensional visualization and analysis

ArcGIS Spatial Analyst

Advanced spatial analysis using raster and vector data

ArcGIS Network Analyst

Routing, closest facility

ArcGIS Survey Analyst

Integrating and managing survey data in GIS

Geographic objects have shapes and size and can be represented as ____, ____, and ____

Polygon, line, point

Polygons

Large things that have boundaries, such as countries, county

Lines

Too narrow to be polygon - rivers, roads, and pipelines

Points

Too small to be polygons - cities, schools, and fire hydrants

Layers may contain ____

Features or surfaces

Raster

- Matrix of identical sizes square cells
- Arranged into rows and columns

Surfaces have ____ values rather than shapes

Numeric

Vector

Points, lines, and polygons

Features

- Have locations
- Can be displayed at different sizes
- Linked to information (attribute tables)

GIS buffers determine what is

- Inside, outside or within a certain distance
- Buffers in 1/2-mile increments around a park

Stream buffers

- Riparian land use within certain distance of streams
- Useful in watershed modeling

Digital Elevation Model (DEM)

- Delineate streams and watersheds
- Create contour lines

New features can be created from ____

Area of overlap

Data requires ____

Management

Spatial data sources may be categorized as either ____ or ____

Hard copy, digital

Hard copy

Drawn, written or printed documents, including hand-drawn maps, measured survey data (all data before 1960)

Digital forms

Spatial data provided in a computer compatible format

Feature map

Simplest and map points, lines and areas

Choropleth map

Quantitative information for areas

Dot density map

Quantitative maps

Contour map

Lines of equal value, also called isopleth maps

Truth map generalization

True rendering of maps

Fused map generalization

Polygons fused together (bunch of small blobs become one big blob)

Simplified map generalization

Polygon detail simplified (rounded approximations instead of sharp angled polygons)

Displaced map generalization

Displaced polygons (increase/decrease distance)

Omitted map generalization

Certain polygons omitted

Exaggerated map generalization

Exaggerated symbols due to standard symbol

Digitizing

Process by which coordinates from a map, image or other sources are converted into a digital format in a GIS

Digitizing points

Represented by digitizing a single location

Digitizing lines

Represented by digitizing an ordered set of points

Digitizing polygons

Represented by set of connected lines

Lines have:

- Starting point (starting node)
- Set of vertices defining the line shape
- Ending node

Digitizing errors

- Not perfectly accurate, human error (lack of verification routines, blunders
- Must be removed or avoided during digitizing

Location errors

- Geometric inaccuracies if spatial features
- Can be checked by referring to the original data source
- Correct it using reshaping or adding new lines

Topological errors

- Errors caused due to violation of the topological relationship
- Digitized features do not follow this relationship will have topological errors