GIS Exam 1

Vector model

Stores discrete data (data that exists in a defined location space)

Vector parts: vertex (each xy pair), nodes (endpoints of lines), multipart features contain separate pieces

Raster model

Stores continuous data (data that has a value everywhere), breaks squares into pixels storing a single value

Feature class

A collection of similar features stored together, like states or rivers

Can only contain one type of geometry

Attribute tables

Show information about spatial objects, each feature has a unique ID (feature ID and object ID)

Map scale

Ratio of distance on map to distance on ground, dimensionless

Some layers can have scale ranges they show at

Generalization

Simplifying features on a map, large scales have less detail

Source scale is the scale at which data is captured

Geometric vs thematic accuracy

Geometric accuracy is how close data is to its actual geometric location, and thematic accuracy is the accuracy of measurements like tree density

Resolution

Sampling interval of measurements during data collection, can be spatial, temporal, or thematic

Storage requirements increase with the square of the resolution: 10 meter takes up 81 times more storage than 90-meter raster

Precision

Number of sig figs in a measurement, or statistical variability of a repeated measurement

Citing GIS Data

Data set name (Year published) [source type]. Producer name, producer contact information.

History of ArcGIS

Arc/Info became ArcView 3 which became ArcGIS then ArcGIS Pro

Panes

Contain commands and settings, movable and stackable

Ex: Catalog, contents, symbology, geoprocessing

Ribbon

Contains buttons and functions organized into logical groups

Ex: map, insert, analysis, view, edit, imagery

Feature layer, labeling, data

Map extent

Can be customized by setting it to a layer or current display extend

Catalog pane

Accesses items in the project folder, portal takes you to online resources, also includes favorites

Layer

Stores properties and settings for display, symbols can be customized and grouped

Symbology

Gallery tab gives you availible styles, properties tab allows you to change settings

HSV Color model

Hue 0-360

Saturation 0-100

Value 0-100

RGB Color model

Values of each primary color from 1 to 255

Nominal data

Names or uniquely identifies objects

Single symbol maps

Categorical data

Places features in categories

Unique values map

Ordinal data

Ranks categories on an arbirtary scale (like low to high)

Uses a unique values map with a single hue color scheme

Interval data

Places values along a regular numeric scale, can have negative values

Ratio data

Places values on a regular scale with a zero point, no negative values, supports all operations

Ex: population

Classed maps

Places features into ranges based on color or symbol size

Graduated color maps, graduated symbol maps

Unclassed maps

Avoid subjective data groupings

Dot density, proportion symbol maps

Modifyable area unit problem

When units are influenced by something else, like # of farms and area or # of vacant houses and population

Minimize by normalizing data through dividing by something

Minimize visual map by not using graduated color

Thematic rasters

May be continuous or discrete, represent map data such as geology and elevation

Displayed with unique values or discrete color display

Stretching

Relocating a smaller portion of the raster values to all 256 shades

Image rasters

Contain photo data that represents brightness

Stretched for single band rasters and RGB composite for multiband

Indexed color rasters

Each value is associated with a specific RGB color combination

Classification methods

Jenks natural breaks, defined/equal interval, statistical (quantile, standard deviation), geometric interval

Map design process

Select, arrange, symbolize, review, edit

Map design considerations

Objective/purpose, audience, medium, data

Cartographic generalization

Simplifying a data set for better map performance

Map grids

Put longitude-latitude marks around a map frame, help measure coordinates

Visual design principles

Visual center (about 5% higher), rule of thirds, alignment, balance, foreground vs background, color vs shape

Layouts

Contain a map frame and include elements like legends and scale bars

Types of text

Graphic text is created on a layout

Dynamic text may be set as properties of a layer

Annotation is created and saved as features in a geodatabase

Reference scale

Allows symbols and labels to get smaller/larger as the map scale changes

Coordinate systems

X/Y/Z values to locate geographic data, said to be georeferenced

A USGS topo map has 3 coordinate systems: latitude-longitude, UTM, and state plane

Unprojected & projected coordinate systems

Unprojected - based on spherical coordinates, measured in degrees of latitude and longitude

Projected - converts spherical coordinates to planar coordinates, projects 3D coordinates onto a 2D map, uses meters or similar units

Geographic coordinate system (GCS)

Stores longitude (east-west angles from the prime meridian) and latitude (north-south angles above the equator), in degrees

Datum

An approximation for earth’s shape used for mapping

Can be local (like NAD) or geocentric/world-centered (like WGS)

Projection

Mathematical conversion of points on Earth’s surface to a flat plane, defined by datum or GCS

Projection types

Cylindrical - preserves direction and shape

Conic - preserves area and/or distance

Azimuthal (planar) - preserves area and/or distance

Projection parameters

Central meridian, standard parallels, latitude of origin, false easting and northing, origin, extend (range of x-y values)

Standard parallels

Where projection touches the ellipsoid

Tangent projection - one standard parallel

Secant projection - 2 standard parallels

Common projections

Universal transverse mercator (UTM) - has 60 N-S oriented zones, preserves all 4 map properties well

State plane system - minimal distortion for parts of states, NS zones use transverse mercator and EW zones use lambert conformal conic

Customizing a projection

Start with a state plane zone or similar, change central meridian and/or standard parallels, you can change false easting or northing if positive xy values are desired

Coordinate system units

Stored units - xy values stored in the file

Map units - determined by CS chosen for the map

Display units - default to map units but may be changed manually

Spatial reference

In properties, labels a CS including storage units, domain, and resolution

Project/define projection tools

Project permanently converts data in one CS to another, creating a new data set

Define projection creates or changes the CS label for unlabeled sets, keeps original dataset

Spaghetti vs topolocigal models

Spaghetti - each state is stored as a separate object, boundaries are stored twice

Topological - stores info about how features are spacially related, including overlap and adjacencies

Managing GIS files

Never use spaces in folder names, organize folders well

Inporting/exporting

Making a copy of a data set, uses export feature class tool

Extracting data

Extracts a subset of data, using queries or a clipping boundary, or erasing features outside a bounding polygon

Merging

Combining features from 2 or more datasets, works best when attribute tables have the same fields but you can also use a fields map function to do it

Appending it similar to merge but adds one set to another and drops all irrelevant fields

Metadata

data about a data set, includes tags, summary, description, credits, use limitation, appropriate scale range, bounding box

Simplifying data

Dissolving - removes boundaries of features with the same value of specified attribute fields

Generalizing - removes vertices and simplifies a set

Geodatabase

Stores data types in ArcGIS Pro

3 types: personal, file, and enterprise (designed for large groups)

Shapefile

Stored in spaghetti data format, can be comprised as many files

Coverages

An old vector format that can be read but must be converted to a shapefile or geodatabase

Pathnames

Absolute (drive letter down) and relative (project file up), used to locate the source of data

Environment settings

Can be used to specify an output location or coordinate system, tools also have an environments tab for just that tool

Raster pyramids

Successively lower resolution copies are created by representing 4 adjacent pixels with a single pixel

Resampling

Changing the resolution of a raster and creating a new copy using a rule to determine new color

Block sampling - uses a statistic

Nearest neighbor - grabs the value from the center of the new cell

Bilinear - calculates value from 4 closest cells

Cubic convolution - calculates new value from 16 closest cells

Bands

A single raster

Multiband rasters can be stacked, common in color photographs

Compression

Reduces storage size, can be reversible or irreversible/lossy such as truncation

Data vs picture rasters

Data rasters store values representing measurements, picture rasters represent color values of a picture or scan

3D Data models

Digital elevation model (DEM) - a raster that stores elevation values

Voxel - a 3D pixel

Point clouds - store x-y-z data, often colored by elevation to store hights, LiDAR is an example

TINs - triangular irregulat networks, store 3D surfaces using fewer nodes for flat areas and more nodes for steep areas

Multipatch features - store 3D shapes to represent buildings

Space time cube - displays xy values as cube stacks by height

raster file types

FGDR, TIFF, ERDAS, GRID, other types can be read and displayed but analyzed or saved

Raster tables

Includes value and count (how many cells have that value), some can have a value of NO DATA #greenland