GIS - After Test 1 Material

Mosiac Tool

Combines multiple raster files into a single raster dataset

Developable Surface

A geometric shape onto which the Earth surface locations are projected

Types of Projection Surfaces

Cylindrical

Conic

Azimuthal (Plane)

What type of projection is Mercator Projection?

cylindrical

How does projection affect x-y values?

Changes from decimal degrees to meters or feet

First step in creating a map projection

Create a point of contact between actual globe and projection surface

Name of point where globe touches projection surface

Point/Line of Tangency

Point/Line of Zero Distortion

Standard Parallel

Point/Line of Contact

Point/Line of True Scale

Standard Line

What is the Central Meridian

The line of longitude that defines the center and often the x-origin of a projected coordinate system.

What is scale on a map?

Ratio of a distance on a map or globe to its corresponding distance on the ground

A measure of projection distortion

Conic Projection

One or Two Points of Contact

Distortion increases at base of cone

Cylindrical Projection

Mercator Projection

Conformal (Shape)

True Direction

What is UTM

Universal Transverse Mercator

Transverse Cylindrical Projection

Azimuth Projection is great for what application?

Polar Projection

Three types of Planar (Azimuth) Projection

Orthographic

Gnomonic

Stereographic

Orthographic Projection

Point of perspective is at infinite distance in opposite direction from point of tangency (from space)

Gnomonic Projection

Point of perspective is located at center of Earth.

Useful for 30° to Poles

Stereographic Projection

Point of Perspective is on opposite surface of globe from point of contact

Useful for a hemisphere

Two most common map projections

Lambert Conformal Conic Projection (Shape Preserving)

Transverse Mercator (Shape and Direction Preserving)

Lambert Conformal Conic Projection

Cone intersects the ellipsoid along two arcs (2 standard parallels)

Preserves Shape

Basis of State Plane Coordinate (SPC) Systems for states with an EAST-WEST orientation (little distortion along standard parallel)

UTM

Universal Transverse Mercator

Developed in 1700s

Basis of pretty much every global map projection

UTM Coordinate System

X and Y coordinates

X - Easting

Y - Northing

METERS

UTM Zones

60 zones

6 degrees longitude wide 8 degrees latitude tall

Zones from 80 degrees South to 84 Degrees North

Each zone is further divided into North and South

What region is excluded by UTM

Polar regions (use azimuthal projection)

How does UTM zone numbering work

1 to 60. 1 starts at International Date Line and travels east around globe. 30 is England

UTM Zone of Alabama

16 North

Grid - 16S

Formula for zone number

Longitude (west is negative, east is positive) + 180° / 6

How do states with multiple UTM zones generate maps?

A UTM like system that places central meridian near center of the state

Coordinates within a UTM zone

All coordinates are positive within the zone

Central meridian is easting 500 km.

Farthest west is 160km. Farthest east is 834 km.

For Northern Hemisphere Equator is Northing 0 Km up to 10,000 km at north pole

For southern Hemisphere equator is Northing 10,000 km and south pole is 0 km

Width of UTM Zone in meters

674000 meters

Pros of UTM

- True Distance Map

- Coordinates are directly tied to distance

- No negative coordinates

- Decimal based coordinates

State Plane Coordinate System

Divide US into 120 zones. Lambert Conformal Conic and UTM projections are the basis.

LCC for East west oriented states (Tennessee)

UTM for North South Orientated States (Alabama)

Minimizes distortion as much as possible

Zones split along county lines.

How many zones does alabama have in the State Plane system

2. East and west

Factors to consider when choosing a map projection

- Purpose (true direction for navigation)

- Extent of area to be mapped (a state versus country)

- Location of region (polar, equator)

- Shape of region (more north south or east west)

Changing Projections

Two step Process

- Invert projection to Lat and Long.

- Transform into new projection system

4 Characteristics of Maps

Scale

Resolution

Accuracy

Projection

Scale

Indicates scale distance of unit on map to real life.

1 inch on map is 1,000,000 inches in real life SMALL SCALE

1 inch on map is 1,200 inches in real life LARGE SCALE

Small Scale

Zoomed way out

Large area little detail

Big number

Large Scale

Zoomed in

Small area big detail

Small number

Map Resolution

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

Small features are hard to represent on a small scale

Map Accuracy

- Flattening round earth onto 2D surface

- Accurately measuring location on Earth

- Digitizing processor error

- Machine precision when storing in computers

ArcCatalog

Arranges and manages geographic information in workspace folders and geodatabases.

ArcMap

the component of ArcGIS used for viewing and analyzing data

ArcToolbox

a suite of tools, available from both ArcMap and ArcCatalog, for analyzing, transforming, and querying geographic data.

Data Frame

a container holding layers that are viewed and analyzed together; a map view

Drawing Order

Layers on top to layer on bottom

Geoprocessing Background

OFF!

If it is on then arc map will crash

Types of GIS objects

Polygons, Lines, Points

How do GIS maps work?

Using layers that contain features (vector) or surfaces (rasters)

Raster

Matrix of identically sized square cells (surfaces)

Record

Row for each feature in layer

Field

Column for each category of information

Buffer

A region around a vector element that indicates distance from that element

Map Forms

Feature Map

Choropleth Map

Contour Map

Quantitative Map

Feature map

Simple map with points, lines, and areas

Choropleth Map

a map that uses differences in shading, coloring to indicate the average values of a property or quantity in those areas.

Quantitative Map

Dot density map

Contour Map

Lines of equal value also called isopleth

Map Generalization

the unavoidable approximation of real features when they are represented on a map.

types of map generalization

Fused - Group features into one big one

Simplified - Smooth edges

Displaced - Separate features slightly for better resolution

Omitted - Small features ignored

Exaggerated - Make bigger to see more details

Digitizing

converting coordinates from a map, image or other source into a digital format in a GIS

Digitizing error

Positional errors are unavoidable when data are manually digitized

Points not snapped together

Location errors

-Geometric inaccuracies of digitized features

-Can be examined by referring to the data source for digitizing

Topological Errors

Errors caused due to violation of topological relationship

Undershoot

Nodes that do not reach the line or another node

Overshoot

Occurs when line cross over existing line or node

Node snapping

Reduce errors by forcing a new point to connect to an existing point

Personal Geodatabase

A geodatabase that stores data in Microsoft Access. A personal geodatabase can be read simultaneously by several users, but only one user at a time can edit the same data.

Multiple files or datasets to store everything

Feature Oriented Editing

Base new features off of an already existing one in the layer

Splitting features

Cut Polygon Features

Sliver polygon

A small, narrow, polygon feature that appears along the borders of polygons following the overlay of two or more geographic datasets. Sliver polygons may indicate topology problems with the source polygon features, or they may be a legitimate result of the overlay.

How to fix sliver polygon

integration tool

Eliminate Tool

Join

Brings spatial and non-spatial datasets together

Requires a common attribute in both datasets

Appends attributes of non-spatial table to layer attribute table

Relate

Simply defines a relationship between two tables but does not append attributes

Temporary connection to access data but keeps tables separate

Relate is appropriate for all four types of relationships

Common Field for Join/Relate

Does not have to be same name, just same data type

(ex. text with text)

How long do joins last

They are temporary and must be exported to be saved

How does join work if there aren't matches

Null values assigned

Four types of relational databases

One to one

One to many

Many to one

Many to many

One to one

Only one record in table is related to another

One to many

One record related to many records

Many to one

Many records in a table related to one record in another table

Many to Many

Many records in a table related to many records in another table

Which relations are best for join?

One to one and many to one

Digital elevation model

Provide elevation data in raster format

Come from ground and aerial survey

Mosiah 3:19

Put off the natural man and become a Saint through the Atonement.

Projection issues with Raster

Project Raster - changes existing projection

Define Projection - no projection exists and create from scratch

Errors in DEM

Sinks or Peaks

Sink

Area surrounded by higher elevation values and is a depression or pit

Peak

Area surrounded by cells of lower value

Terrain Preprocessing

1. Fill Sinks

2. Flow Direction

3. Flow Accumulation

4. Watershed Outlet

5. Watershed

Fill Sink

Remove small imperfections in raster DEM data

Flow direction

Raster of flow direction from each cell to its steepest downslope neighbor

32 64 128

16 X 1

8 4 2

Flow accumulation

Calculates accumulated flow as the weight of all cells flowing into each downslope cell in the raster

Watershed outlet

Snap point for raster set to know where the specified boundary of watershed should be drawn

(If you choose a point up stream will have multiple smaller watersheds)

Extract by Mask

Extract cells of raster based on area defined by mask

4 fundamental classes of raster functions

Local

Focal

Zonal

Global

Local raster function

Only looks at each cell individually

(could be multiple layers stacked ontop of each other from temporal data and get average)

Focal raster function

Function of a cell and its surrounding neighborhood of cells

Operation involves cells contained given window

Overlapping

4 common neighborhood shapes

Rectangular - most common

Circle

Annulus - doughnut

Wedge - directional component

Zonal raster function

Similar to zonal but now zone is all cells with a similarly shared given value (can also be a mask)

Can be contiguous or noncontiguous

Block functions

Neighborhood function that assigns one value to all cells within a moving, non-overlapping neighborhood or block.