GIS II Textbook Definitions EXAM 1

Single-Part Feature

A single geographic object for each row in the attribute table

Multi-Part Feature

Spatially distinct features that are matched with a row, and the row attributes apply to all the distinct features.

Polygon Inclusions

Areas in a polygon that are different from the rest of the polygon, but still a part of it.

Boundary Generalization

The incomplete representation of boundary locations

Minimum Mapping Unit

The lower limit on the size of the objects we care to represent in our data

Nodes

Line starting and end points, also points where they intersect when topology is applied.

Vector Topology

Enforcing strict connectivity and recording adjacency and planarity.

What is the point of topology?

Maintains relationships between spatial data

Planar Topology

Requires that all features occur on a two-dimensional surface. No overlaps. At each line crossing there must be an intersection marked with a node.

Adjacency

Which lines are next to which.

Dangle

Lines that DO NOT connect to other lines

What is the distinct aspect of Discrete Data

Has borders where data either exists or does not exist

What is the distinct aspect of Continuous Data

Has data values at any given point, example: elevation

How is cell size measured?

The area the pixel covers on the ground in real life.

If a pixel resolution is 30 units, what is the cell size?

900 square units

What are the characteristic of data with a small cell size?

Higher resolution, higher feature spatial accuracy, slower display and processing, larger file size.

Pixel Depth

Determines the range of values that a particular raster file can store

What do we put in place of cells that have an absence of data?

NoData cells

NoData in = ___?

NoData Out

What do we call the two broad categories of data compression?

Lossy and Lossless

Data compression where all data is maintained:

Lossless

Data compression where some data is lost:

Lossy

Which data compression method is most often applied to discrete raster data?

Lossy

Quadtree Coding

Stores the information by subdividing a square region into quadrants, each of which may be further subdivided into squares until the contents of the cells have the same values.

Run-Length Coding

Common data compression method where running characters are simplified to just two characters. Example: AAAAA → A5

Pyramiding

Creates pyramids to increase display speeds when viewed at small scales, not a data compression type. Usually increases files size.

Many-to-One

Many raster cells are allowed to refer to just one row in the attribute table which reduces the data size greatly at the cost of some spatial ambiguity. Often creates multi-part areas

One-to-One

Can easily result in huge data sizes making simple functions extremely time consuming and decreases the likelihood the GIS will be applied effectively

Why does cell size matter in vector to raster conversions?

To ensure that features are distinct form one another

How do they choose the cell size in vector to raster conversions?

So that the diagonal cell dimension is smaller than the distance between the two closest point features.

What processes often need to happen when converting vector to raster?

Resampling of data and reassigning the cell values

Bilinear Interpolation

Distance based averaging of the four nearest cells.

Cubic Convolution

Weighted average of the sixteen nearest cells.

Convergent Circle

A circle passing ONLY through three points to create the varying triangle types in the TIN network.

What makes TIN better than Raster?

It works better visually and is often more efficient for terrain data in highly variable areas.

In the TIN, what do areas of larger triangles indicate?

More homogeneous data, ex. terrain that has a gentler slope.

Logical Model

The user view of the real objects we portray with GIS

Inheritance

Automatically transferring properties within classes of objects.

Voxels

Volume elements, essentially cubes of a fixed dimension.

Reality Mesh

Combines TIN model with an image-based texture surface to create realistic representations of 3D features.

Bit

Each digit or column in a binary number

Byte

8 columns/bits

What does the ASCII stand for?

American Standard Code for Information Interchange

What does the ASCII do?

It is a standardized, widespread data format that uses seven bits to represent text and other characters. Used for data export and exchange

What does the ANSI stand for?

American National Standards Institute

What does the ANSI do?

It’s a standardized data format just like the ASCII except there is extra binary bits. Used for data export and exchange.

Pointer/Index

Address or index that connects one file location to another, a way to organize information.

what is the topology rule for Arc Nodes

Line features can share endpoints

What is the topology rule for Polygons

Area features can share boundaries

What is the topology rule for Routes

Line features can share segments with other line features

What is the topology rule for Regions

Area features CAN overlap with other area features.

What is the topology rule for Nodes

Line features can share endpoint vertices with point features

What is the topology rule for Point Events

Point features can share vertices with line features

Describe a File Geodatabase

A collection of GIS databases is stored in a file system folder. Can support multiple people operating with different feature classes at the same time. Often with ArcPro

Describe an Enterprise Geodatabase

Supports versioning and replication. Requires a database management system. Supports unlimited users editing and viewing at the same time with an unlimited database size.

Coarse Resolution Sensor

Pixel dimension of 250 m or larger

What does VIIRS stand for?

Visible Infrared Imaging and Radiometer Suite

What is VIIRS and what is it used for?

An instrument created to collect data for weather, ocean, and land surface analysis.

What is Sentinal as it relates to Satellite Imagery?

A mission launched by the European Space Agency made up of 6 missions, 12 spectral bands. The data is free with a 5 day global frequency.

Where is the visual center of a map?

5% above the geometric center of the map

Stream Sampling Digitizing

Automated sampling at a fixed time or distance frequency

Minimum Distance Digitizing

A new point is not recorded unless it is more than some minimum threshold distance from the previously digitized point. The distance is set by the user to avoid being too large to miss detail and too small to revert to stream sampling efficiency.

Undershoots

When digitizing, these are nodes that do not quite reach the line or another node.

Overshoots

In digitization, these are lines that cross over existing nodes or lines

Snapping

A function in digitization, the process of automatically setting nearby points to have the same coordinates. Relies on snap tolerance / snap distance. If nodes are within that distance, they are moved to occupy the same location.  

Spline

Set of polynomial functions that join smoothly. (smoothing digitized lines to appear more curved) 

Skelotonizing

Line thinning, particularly when converting from vector to raster where line positioning ends up with fat lines in raster format if the location isn’t directly in the center of the cell.  

Rubbersheeting

Fitting a local equation to adjust the coordinates of features. Anchor points are selected and the other points involved can be retrofitted for adjustments

Slivers

Small gaps or overlaps along shared polygon boundaries. Most often occurs when snapping distance is set too short.  

Metadata

Data about digital data. Information about spatial data that describes the source, lineage, methods, developer, coordinate system, extent, structure, spatial accuracy, attributes, and responsible organization.  

Rows in a table are also known as? 2 answers

Records or Tuples

Keys

One or more columns that meet certain requirements and may be used to index the rows. Often a column that uniquely identifies every row in a table. They are used to join tables together.

What is something that is not allowed to be a part of a key?

Null values

If there are many potential key columns, but we still select one key, what do we call this selected column?

Primary Key

When multiple columns are used together as a key

Concatenated Key

How many columns are typically involved in a concatenated key?

Typically 2, rarely more than 3

Schema

A compact graphical representation of the conceptual model, the entities, tables, keys, and the relationships among them. 

What does FIPS stand for

Federal Information Processing Standard

How is FIPS used?

Every county within a US state assigned a unique code but unique only within the state. Need both state ID and cFIPS ID to identify.  

Foundational Table

Original table to be used to create a table join.  

Output Table

Resulting table of a table join.  

What does a join operation do?

It combines two tables through keys where values in one or more keys are matched across tables.

Query

The selection (or restriction ) of a subset of records based on the values of specified attributes.  

Specify what the AND condition covers

Select records that meet 2 criteria. Creates a more strenuous set of conditions that must be met, typically reducing the selected material.  

Specify what the OR condition covers

Adds records that meet a criterion to a set of records defined by previous criterion which typically increases the selected material.  

Specify what the NOT condition covers

The negative operation, ‘do not show me this’ 

What does SQL stand for

Structured Query Language

What is the function of SQL?

Non procedural query language in that the specification of queries does not depend on the structure of the data. Long or complicated queries may be saved, which can be described as programs given their complexity. 

What are some reasons to keep tables on the smaller side when possible?

Large tables make for slow queries and difficult updates. Selection is easier with smaller tables and its easier to know that all of the data is useful.

Normal Forms

Data are structured in sequentially higher normal forms to improve correctness, consistency, simplicity, non redundancy, and stability.  

Functional Dependency

Attributes are functionally dependent if at a given point in time, each value of the dependent attribute is determined by a value of another attribute.  

What are three rules of functional dependency

There cannot be repeated records, no rows where all attributes are equal. There must be a primary key in the table. No member of a column that forms part of the primary key can have a null value.

To Normalize

When a table is placed in to normal forms which typically results in multiple compact, linked tables.  

First Normal Form 1NF

When a table has no repeat columns. Most basic level of table normalization.

Second Normal Form 2NF

If first in 1NF and every non-key attribute is functionally dependent only on the primary key. To create, we make every non-key attribute fully dependent on a primary key in the new tables, usually splitting the foundational table into more tables

Third Normal Form 3NF

If for every functional dependency A->B, where A is a super key, or B -> is a member of a candidate key.  

Super Key

Any set of one or more attributes (columns) that uniquely identifies a record (tuple) in a table. It can contain extra, redundant attributes.

Primary Key vs Super Key

Not every super key is a primary key but every primary key is a super key.

Candidate Key

A minimal super key, meaning it uniquely identifies a record, and if you remove any attribute from it, it loses that unique identification property. 

Can you have null values in a primary key?

No