LDA 150 Midterm 1

Thematic Layer

A map designed primarily to show a theme or a single spatial distribution or pattern, using a specific map type.

Coordinate System

A system with all the necessary components to locate a position in two or three-dimensional space; an origin, a type of unit distance and axes.

Latitude

Centered on the equator, run E-W

Longitude

Centered on prime meridian, run N-S

Projection

A depiction of the earth's three-dimensional structure on a flat map.

Datum

Mathematical representation of a projection

Spheroid

Like an ellipsoid, an oblated sphere

Geoid

A representation of the earth based on strength of gravitational pull towards center of the earth.

Coverage

a georelational data model that stores vector data—it contains both the spatial (location) and attribute (descriptive) data for geographic features

Shapefile

A raster dataset

Integer Raster

Stores cell data as integer values (whole numbers)

Floating Point Raster

Stores cell data with decimal points

Slope

Rise over Run

Aspect

Which direction a mountain slope faces the sun

Hillshade

Use of an apparent shading effect of raised topography so that the land surface appears differentially illuminated, as it would in low sun angles naturally.

Feature Attribute Table

A database or tabular file containing information about a set of geographic features, usually arranged so that each row represents a feature and each column represents one feature attribute

Map Document

A depiction of all or part of the earth as a set of symbols and a scale whose fraction is less than 1:1. A digital map has all features geocoded and stored as data structure within the map database.

*.SHP

Shapefile

*.DBF

Database File

*.SHX

Shapefiel

*.PRJ

Projection File

*.MXD

ArcGIS file

Primary Key

The key that has unique identifiers that allows two maps to be joined.

Foreign Key

An attribute or set of attributes in one table that match the primary key attributes in another table

Schema

The structure or design of a database or database object, such as a table, view, index, stored procedure, or trigger.

Data Model

a mathematical construct for representing geographic objects or surfaces as data.

NAD27

A North American focused coordinate system

NAD83

A geographic coordinate surface with center in middle of earth

Contour Interval

lines of equal elevation set equidistant from one another

Summary Table

TOC

Table of Contents on top left of ArcGis

Transverse Projection

A projection in which the axis of the map is aligned from pole to pole rather than along the equator.

Secant Projection

A projection in which the surface used for the map cuts the globe at the map's representative fraction. Along this line there is distortion-free mapping of the geographic space.

Line Weight (Map Symbology)

GIS (2 main components)

A computer system that connects spatial data with attribute data

Table Joining

A table join occurs when a source table is linked to a target table using a unique field located in both tables.

Geodetic Datum

A coordinate system and set of reference points used to determine the location of places on the earth.

Earth Centered Datum

WGS 1984 (World Geodetic System)

Local Datum

NAD 1983 (North American Datum)

Spatial Query

Polygons of layer x completely contain points of layer y.

7.5' USGS Quadrangle Map (DOQ)

Standard topographic map of entire US with an RF scale of 1:24,000. Has UTM and state plane coordinates.

DOQQ (Digital Orthopohoto Quarter-Quadrangle)

3.75' quarters of raster data and aerial footage on a scale of 1:12,000.

Raster Data

Large shape files, made up of uniform grids (pixels). Overlay operations are more efficient with raster data.

Vector Data

Composed of points, lines and polygons (organizes geometric objects and spatial relationships). Works best at outline precise boundaries by using x-y coordinates to represent discrete features.

Resolution (For Raster)

Resolution is determined by the number of pixels in a raster. The resolution also determines the location and shape of geometric data.

TIN

Triangular Irregular Network uses triangles to show topography and surfaces. Has a topological data structure.

Dissolve Function

The function that allows boundaries or lines to be removed from a set.

Clip Function

The function that clips one layer to the size of another but does not alter the attributes of the input layer.

Main ArcGis Software

Composed of ArcCatalog, ArcMap, and ArcToolbox

Main Graphic Elements of a Map

1. Title

2. Name

3. Legend

4. Scale bar

5. North Arrow

6. Sources

7. Projection

8. Date

Ways Map Projections Distort

1. Shape

2. Area

3. Distance

4. Direction

Conformal Projection

Projection that preserves local shape, but loses area

Equal Area Projection

Projection that preserves area, but loses shape

GCS (Geographic Coordinate System) (and units)

Uses 3D spherical surface to define points on earth. A GCS has an angular unit of measure, prime meridian, and a datum usually based on a spheroid. Units are typically based in radians, DMS or DD.

GRS80

A geodetic reference system sitting of a global reference and a gravity field model.

UTM (Universal Transverse Mercator)

Splits world into 60 zones, 6 degrees apart from 80S to 84N. Measured in northings and eastings and in meters. A cylindrical, conformal projection is rotated to get the best fit for each zone.

Project vs Define Projection

Project changes the projection and shape, Define Projection creates a .prj file.

Project-on-the-fly

This means ArcMap can display data stored in one projection as if it were in another projection. The new projection is used for display and query purposes only

Database Field Types (6)

1. Text

2. Double

3. Short Integer

4. Long Integer

5. Float

6. Date

Multi-part Feature

Layer File

Feature

A representation of a real world object on a map

Feature Class

A collection of the same type of geometry.

Feature Dataset

A collection of related feature classes that share a common coordinate system. Used for organizing data in a dataset.

Topology (and fundamental concepts)

1. Every arc has 2 nodes (a beginning and an ending)

2. Every arc separates two polygons

3. Every polygon is surrounded by a cycle of nodes and arcs.

4. Every node is surrounded by a cycle of arcs and polygons.

5. Every intersection is at a node.

Fundamentals: Connectivity, containment and adjacency.

Common Topological Errors (>3)

1. Dangle

2. Overshoot

3. Overlap

4. Slivers