Jensen Chapter 5

feature class

A collection of geographic features with the same geometry type (such as point, line, or polygon), the same attributes, and the same spatial reference.

class

A collection of objects with the same attributes.

vector data structure

A coordinate-based data model that represents geographic features as points, lines, and polygons. Each point feature is represented as a single coordinate pair, while line and polygon features are represented as ordered lists of vertices. Attributes are associated with each vector feature, as opposed to a raster data model, which associates attributes with grid cells.

relational database

A data structure in which collections of tables are logically associated with each other by shared fields.

geodatabase

A database or file structure used primarily to store, query, and manipulate spatial data. Geodatabases store geometry, a spatial reference system, attributes, and behavioral rules for data. Various types of geographic datasets can be collected within a geodatabase, including feature classes, attribute tables, raster datasets, network datasets, topologies, and many others. Geodatabases can be stored in IBM DB2, IBM Informix, Oracle, Microsoft Access, Microsoft SQL Server, and PostgreSQL relational database management systems, or in a system of files, such as a file geodatabase.

enclosure

A file describing the contents of an item included in metadata. Enclosing files in metadata works the same way as enclosing files in an e-mail message.

class intervals

A set of categories for classification that divide the range of all values so that each piece of data is contained within a nonoverlapping category.

value attribute table

A table associated with a raster dataset that describes the number of times that a cell value occurs in a dataset.

adjacency

A type of spatial relationship in which two or more polygons share a side or boundary.

primary key

A unique identifier used to relate databases.

object-based vector model

A vector data model that uses objects to store both spatial and attrubute data in a single system.

shapefile

A vector data storage format for storing the location, shape, and attributes of geographic features. A shapefile is stored in a set of related files and contains one feature class.

Structured Query Lanuage

Acronym for Structured Query Language. A syntax for retrieving and manipulating data from a relational database. SQL has become an industry standard query language in most relational database management systems.

many-to-one relationship

An association between two linked or joined tables in which many records in the first table may correspond to a single record in the second table.

one-to-many relationship

An association between two linked or joined tables in which one record in the first table corresponds to many records in the second table.

one-to-one relationship

An association between two linked or joined tables in which one record in the first table corresponds to only one record in the second table.

many-to-many relationship

An association between two linked or joined tables in which one record in the first table may correspond to many records in the second table, and vice versa.

coverage

An older data model for storing geographic features. It stores a set of thematically-associated data considered to be a unit. It usually represents a single layer, such as soils, streams, roads, or land use. In a coverage, features are stored as both primary features (points, arcs, polygons) and secondary features (tics, links, annotation). Feature attributes are described and stored independently in feature attribute tables.

relate

An operation that establishes a temporary connection between records in two tables using a key common to both.

join

Appending the fields of one table to those of another through an attribute or field common to both tables. A join is usually used to attach more attributes to the attribute table of a geographic layer.

ordinal data

Data classified by comparative value. for example, a group of polygons colored lighter to darker to represent less to more densely populated areas.

interval data

Data classified on a linear calibrated scale, but not relative to a true zero point in time or space. Because there is no true zero point, relative comparisons can be made between the measurements, but ratio and proportion determinations are not as useful. Time of day, calendar years, the Fahrenheit temperature scale, and pH values are all examples of interval measurements.

ratio data

Data classified relative to a fixed zero point on a linear scale. Mathematical operations can be used on these values with predictable and meaningful results. Examples of ratio measurements are age, distance, weight, and volume.

nominal data

Data divided into classes within which all elements are assumed to be equal to each other, and in which no class comes before another in sequence or importance; for example, a group of polygons colored to represent different soil types.

raster data structures

Geospatial data stored in a raster (matrix) format where each picture element (pixel) is associated with a row and column of the raster dataset.

raster layer

In ArcGIS, a layer that references a raster as its data source and a raster renderer that defines how the raster data should be rendered and any additional display properties.

raster dataset

In ArcGIS, a raster spatial data model that is stored on disk or in a geodatabase. Raster datasets can be stored in many formats, including TIFF, Imagine, ESRI Grid, and MrSid.

data model

In GIS, a mathematical construct for representing geographic objects or surfaces as data. For example, the vector data model represents geography as collections of points, lines, and polygons; the raster data model represents geography as cell matrixes that store numeric values; and the TIN data model represents geography as sets of contiguous, nonoverlapping triangles.

node

In a geodatabase, the point representing the beginning or ending point of an edge, topologically linked to all the edges that meet there.

topology

In geodatabases, the arrangement that constrains how point, line, and polygon features share geometry. For example, street centerlines and census blocks share geometry, and adjacent soil polygons share geometry. Topology defines and enforces data integrity rules (for example, there should be no gaps between polygons). It supports topological relationship queries and navigation (for example, navigating feature adjacency or connectivity), supports sophisticated editing tools, and allows feature construction from unstructured geometry (for example, constructing polygons from lines).

vertex

One of a set of ordered x,y coordinate pairs that defines the shape of a line or polygon feature (betyween the beginning and ending node).

SQL

See Structured Query Language

vector-to-raster conversion

The act of converting points, lines, or polygons into a raster data format.

raster-to-vector conversion

The act of converting raster data to points, lines, or polygons.

foreign key

The field in a second database that links with the primary key to combine two or more databases.

classification

The process of sorting or arranging entities into groups or categories; on a map, the process of representing members of a group by the same symbol, usually defined in a legend.

connectivity

The way in which features in GIS data are attached to one another functionally or spatially.

common key

When the primary key and the foreign key have the same field name in each database