GIS Mid-Term Exam Vocab

What is spatial data?

• Many different formats

• Includes location information

• Any information with a location attached to it.

Why is it special?

• Multidimensional

• Voluminous

3 basis of classifying problems:

• Scale or level of geographic detail

• Intent or purpose

• Time scale

3 principles of spatial variation:

• Proximity effects are key to representing and understanding spatial variation.

• Issues of geographic scale and level of detail are key to building appropriate representation.

• Different measures of the world co vary

Positive spatial auto correlation

If the features that are similar in location are also similar in attributes.

Negative spatial autocorrelation

Features that are close together in space tend to be more dissimilar in attributes than features that are further apart. (Checkerboard pattern)

Zero autocorrelation

When attributes are independent or no definite neighbor.

Discrete data

Real world features with well defined boundaries

ex. river, buildings, streets, ocean.

Continuous data

Do not have well defined boundaries.

ex. elevation, rainfall, temp.

Vector

Distance and direction from a location.

• Vector data model represents discrete objects on the surface of the earth.

• ex. roads buildings

Raster

• Data models stores information in rows and columns

• Attributes are represented in a cell.

Data types

• continuous raster

• discrete data

• imagery

• scanned map

Remote sensing

Acquiring data with sensor systems that digitally record the interaction between electromagnetic energy and object.

Advantages of this:

• consistency of the data

• availability. of systematic global change

• regular repeat cycles

Metadata

Data about the data:

• Primary collector of the data

• Description about the content

• Range of possible values

Map scale

Scale of a map or data is the size of a map or data on a screen or printed paper relative to the size of it in real world.

ex. 1 cm on the map = x cm on the ground

Geodatabase

Physical store for your GIS data.

3 types:

• Personal geodatabase

Stored and managed in microsoft access data files and has maximum size of 2 GB. Can be read by multiple people, but only edited by one person at a time

• File geodatabase

Stored in the file system folder, up to 1 tetrabyte. Supports multiple people editing different features classes or tables at the same time.

• Multiuser geodatabase

Support versioning and replication, requires a data base management system. Found in larger organizations because it supports multiple viewers and editors.

Feature classes

Thematic datasets representing geographic features, tables with a spatial field and and additional column.

Feature datasets

Store spatially related feature classes in a common dataset for building topology.

Mosaic dataset

Manages large collection of raster data which can be heterogenous in:

• Format

• Source

• Data type

Cartesian coordinates

• 2 dimensional

• expressed in ordered pairs

• axes are perpendicular

Datum

Coordinates without specified datum are vague.

• How is it defined?

Using 1 of the spheroids

Using latitude and longitude

Two most common spheroids:

• GRS80

• Clarke 1866

Latitude (Parallel)

Gives you the extent a particular point lays north or south of equatorial plane.

• Positive —> north of the equator

• Negative —→ south of the equator

Longitude

Gives the same east or west of prime meridian.

• Positive —→ east of the prime meridian

• Negative —→ west of the prime meridian

NAD 1927

Obtained from ground based measurements. Is not geocentric center of the reference ellipsoid and center of mass of planet are no coincident.

North American Datum 1983

3-D geometric datum

Further upgrade continuously operating reference stations NAD 83.

3 main elements in coordinate systems:

1. Name

2. Units of measure

3. Datum

Geographic coordinate system

Spheroid (ellipsoid)

Angular units (degrees)

• Difficulties

Units of degree cannot be used to measure distance on the ground, or the length of a line.

Reference globe

Created by wrapping a grid of lines or graticules around a model of the earth.

Projection

The process of converting a round globe into a flat map.

Small and large areas:

Small areas: flat earth approximation works well.

Large areas: flat earth introduces distortion which causes errors.

Scale factor

The amount of distortion when the surfaces of a spheroid is projected onto a plane is defined by scale factor (k).

k = distance on the projection / distance on ellipsoid

2 types of distortions:

1. kp = along parallel

2. km = along meridian

3 types of projection:

1. Equidistant - preserving distance along meridian.

2. Equal area - area preserved

3. Conformal - shape preserved

Distortion

1. Shape *conformal

Feature outline look the same on map as they do on the earth.

2. Area *equal area

The size of feature on a map is the same relative to its size on the earth.

3. Distance *equidistant

Line on map has same relative distance with the line on the earth.

4. Direction *azimuthal

Useful for navigation

Developmental surfaces

A geometric shape that can be flattened without being distorted (cone, cylinder, plane)

Point of tangency

A plane touches the globe at a single point.

Secant

Line of intersection between the globe and the surface.

Cylindrical

Touches globe along a line called a tangent, or it can pass through the globe and intersect along 2 secants

Meridians straight, meridians and parallels intersect at right angles

Conic

Created by setting a cone over a globe and projecting light from the center of the globe onto the cone.

Contacts the globe along a single tangent.

Standard parallel

Line of latitude in conic or cylindrical projection where projection surface touches globe.

Central meridian

A line along which the developable surface is cut and flattened into a plane.

Transverse mercator

Cylinder touches the sphere along a meridian. A conformal map projection good for north-south extending areas.

State plane coordinate system

Relies on imaginary flat reference surface with cartesian axes.

Calculates easier

Has zones and is a standard map projections within U.S.

Conformal projection

UTM coordinate system

conformal projection

divides earth into 60 zones, each zone is 6 degrees

3 primary requirements of georeferencing are:

1. unique - only 1 location associated with a given georeference.

2. Shared meaning - meaning is shared among all users.

3. persistent through time - addresses change.

Geocoding

Matching of an address with its corresponding geospatial location.

Baton geocoding

Multiple addresses can be plotted at the same time and mapped as a point feature class.

Address locator

Rules for interpreting addresses list of standard street components snap shot of reference data.

Reference data

Snapshot of geographic data with address information.

Georeferencing

Process of registering your source imagery to a reference image or vector GIS layer. Defining location to your unknown spatial reference data using map coordinates and assign the coordinate system.

Target data

Geoferenced raster or a vector feature class that resides in the desired map coordinate system.

Source data

Data with unknown coordinate system.

Polynomial transformation

Uses least square fitting algorithm order of polynomial.

Spline

True rubber sheeting

• Optimizes for local accuracy but not global accuracy.

Root mean square error

The difference between where the from point ended up as opposed to the actual location that was specified to point position.

RMSE: Describes how consistent the transformation is between links.

Attribute tables

Spatial data store more than just their spatial properties. Non-spatial information about spatial features make up the attribute table.

Different types of attributes

1. Nominal data

2. Ordinal data

3. Interval data

4. Ratio data

Attribute join

Linking two or more tables. Can only be preformed if 2 tables have a field in common called as key.

One-to-one

Single record is linked to another single record.

Many-to-one

Many records in an attribute table is joined to 1 record from another table.

For making queries:

• If and is used, then BOTH must be true

• If or is used, then either may be true.

Boolean operators

Used to evaluate pairs of conditions.

Spatial analysis

Finding distributions and pattern of features.

Spatial distribution

Finding spatial distribution of something.

Overlay

Two or more layers, overlay analysis is needed.

To find locations that are suitable for particular use or are susceptible for some risk.

Map overlay

Combines two or more layers to create a new output feature class containing information from both.

Geoprocessing

When two or more functions are applied together to solve a specific problem.

Types of overlay:

1. Point-in polygon

Use to assign polygon attributes to points.

2. Line-on polygon

Use to assign polygon attributes to lines.

3. polygon-on polygon

New spatial data is created with features and attribute table.

Union

Combines and keeps all features.

Intersect

Combines and keeps common features.

Dissolve

Eliminates all of the attributes in the table except the dissolved one.

Buffer

Constructs polygon areas within a specified distance of features.

Merge

Combines 2 features classes of the same type into a new combined feature class.

Near

Calculates distance between the input features and the closest feature in another layer or feature class.

Append

Places features from 1 feature class into a existing feature class of the same type.

Tagged image file format (TIFF)

Geotiff tags are supported. Supports black and white + gray scale

Joint photographic experts (JPEG)

A standard compression technique for storing full color and gray scale images.

Portable network graphic (PNG)

Provides a well compressed lossless compression for raster files.

Local operations

Examines raster by cell. Achieved using map algebra.

Zonal operations

Compute results for blocks of contiguous cells that share the same value.

Global operations

Produce results that are true of the entire layer such as mean value.

Euclidean distance

Operation assigns to each cell its distance from the closest source cell.