AGRI270 Quiz Two Ch 5 - 8

Vector Data Model

• Discrete objects with sharp edges

• Points, lines, and polygons

• Roads, wells, parcels, boundaries

Raster Data Model

• A continuous grid of cells

• Every cell holds a value

• Elevation, land cover, temperature

Points

Single locations - a well, a tree, a fire hydrant, a GPS reading

Points

Lines

Connected Points - roads, rivers, pipelines, trails

Lines

Polygons

Closed Areas - parcels, lakes, buildings, county boundaries

Polygons

Digitizing

Creating vector features by tracing points, lines, and polygons from a source - a map or an image

Heads-up digitizing

Tracing on screen directly over aerial or satellite imagery - the most common method today

National Hydrography Dataset

The USGS NHD maps the nation’s water - streams, rivers, canals, lakes, ponds, and coastlines - as vector features.

Lines and polygons with attributes

Flowlines (streams, canals, pipelines) are lines; waterbodies (lakes, reservoirs, swamps) are polygons - each typed by FType.

National Land Cover Database (NLCD)

Database that classifies every 30m cell of the U.S. into land cover types - water, forest, developed, crops, wetlands, etc.

Vector

• Discrete Objects with crisp boundaries

• Compact; exact shapes and lengths/areas

• Best: Parcels, roads, wells, boundaries

• Attributes rich per feature

Raster

• Continuous surface of equal cells

• Simple structure; heavier files

• Best: elevation, land cover, imagery

• One value per cell

Nominal

Names/categories, no order.

Land-use type, ZIP code.

Ordinal

Ranked order, unequal gaps.

1st/2nd/3rd; low/med/high.

Interval

Ordered, equal gaps, no true zero.

Temperature (°F).

Ratio

Ordered, equal gaps, true zero.

Distances, dollars, acres.

Records

Each row is one feature - one parcel, one county, one stream segment

Fields

Each column is one attribute - name population, area, land-use code

Metadata

Descriptive information about a dataset - usually a readme or XML file.

ArcGIS Pro

Esri’s flagship desktop GIS - the modern professional application for mapping and analysis

ArcGIS Online

A cloud/web GIS for making and sharing maps in a browser

ArcMap (Legacy)

The older desktop product many organizations still run, now succeeded by ArcGIS Pro

Geodatabase

A container that holds all the layers and tables for a project in one place

Feature classes

Each layer of one geometry type - A highways layer, a parcels polygon layer, a wells point layer

Feature Datasets

Group related feature classes that share a coordinate system

Python

The main GIS scripting language - readable, everywhere, and the tool both ArcGIS and QGIS automate with

QGIS

A free, open-source desktop GIS with most of the capability of paid packages

Query (SQL)

Selects the features whose attributes meet a conditions

Boolean Operator

A word _ AND, OR, or NOT - that joins two or more conditions into a single compound query

Intersection Query (AND)

Returns only records that meet BOTH conditions

Union Query (OR)

Returns records that meet EITHER condition

Negation (NOT)

Returns the records that do not meet a condition

Select by Attribute

• Query the table

• ‘Which parcels are zoned commercial’

• Answer comes form the data values

Select by location

• Query by spatial relationship

• ‘Which parcels are WITHIN 500m of the river’

• Answer comes from geometry and position

Buffer

A new polygon covering everything within a chosen distance of a feature - around points, lines, or polygons

Intersect

Keep only where BOTH layers overlap

Union

Keep everything from both layers

Identity

Keep the input layer, split by the overlay

Symmetrical Difference

Keep only the parts that don’t overlap

Intersect

What vector overlay?

Identity

What vector overlay?

Symmetrical Difference

What vector overlay?

Union

What vector overlay?

Combine Layers

Overlay merges two or more layers so you can find where their conditions occur together

Reclassify

Assign new values to raster cells - often grouping many values into a few meaningful classes

Cell-by-cell math

Map algebra combines rasters with arithmetic - add, subtract, multiply - matching cell to cell

Boolean rasters

Map algebra combines grids with logical operators

Site suitability modeling

Score each location based on several criteria, then combine the scores to rank every place from worst to best

Hot spot

A statistically significant cluster

Geoprocessing

Chaining tools into a workflow

Map

A representation of spatial data that conveys information to its reader - the end product of your GIS work

Cartography

The science and art of mapmaking

Visual Hierarchy

How features are displayed to emphasize their level of prominence

Geographic scale

The real-world size or extent of an area

Representative fractiion

Expresses map scale as a ratio

Large-scale map

• Larger representative fraction value

• Shows a smaller geographic area

• More detail - buildings as polygons

• largest possible is 1:1

Small-scale map

• Smaller representative fraction value

• Shows are larger geographic area

• Less detail - cities as points

Scale Bar

A graphical device that represents the map’s scale

North Arrow

A graphical device that can help understand a map’s orientation

Legend

A graphical device that explains what the map’s various symbols and colors represent

Reference Map

• Shows the locations of features.

• Road maps, atlases, topographic maps.

• Answers: “where are things?”

Thematic Map

• Conveys one particular theme

• ‘State-by-state population changes’

• ‘2020 election results by county’

• Answers: “how does one thing vary?”

Choropleth

Colors existing areas by a value to show it well

Graduated Symbols

Different sized symbols convey a thematic quantity

Natural Breaks (Jenks)

Sets class breaks at natural gaps in the data values

Quantile

Puts an about equal number of features in each class

Equal Interval

Divides the total value range into equal-width classes

Standard Deviation

Sets breaks by the mean and how far values sit from it

Network

A series of junctions and edges connected together to model things like streets

Junction

A node - a place where edges come together (intersections, on-ramps, endpoints)

Edge

A link of the network - the line that represents a road segment

Connectivity

The linkages between edges and junctions - what connects to what

Street Centerline

A file of line segments representing roads - one record per small road segment

Line segment

A single edge of the network - one section of a street between junctions

Topologically Integrated Geographic Encoding and Referencing (TIGER)

Free U.S. Census Bureau files of road segments

Geocoding

Using the text of an address to plot a point at that location on a map

Reference Database

The base network data used as the source for geocoding

Parse

Break the address into its component parts

Standardize

Put the address components parts into a consistent format

Linear Interpolation

Places the address among the range along a segment

Batch Geocoding

Matching a whole list of address at once

Transit Cost (impedance)

How many units - miles or minutes - it takes to traverse an edge

Shortest Path

The route with the lowest cumulative transit cost between stops

Dijkstra

The algorithm that finds the lowest-cost path from an origin to destinations, and then writes turn-by-turn directions