GIS Glossary/L

GIS Glossary

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label
In cartography, text placed on or near a map feature that describes or identifies it.

label class
In ArcMap, a category of labels that represents features with the same labeling properties. For example, in a roads layer, label classes could be created to define information and style for each type of road: interstate, state highway, county road, and so on.

label engine
In ArcMap, the software used to place labels.

label expression
A statement that determines the label text. Label expressions typically concatenate or modify the contents of one or more fields, and may add additional text strings to create more informative labels. They can contain Visual Basic script or JScript to add logic, text processing, and formatting for the labels.

Label Fitting Strategy tab
In Maplex for ArcGIS, a tab on the Label Placement dialog box that allows control of the ways the label engine can fit more labels into a limited area. Methods that can increase label placement are stacking labels, reducing the font size of labels in congested areas, or abbreviating labels.

Label Manager
In ArcMap, the tool used to display and set labeling properties for the currently active data frame. The Label Manager is accessible through the Labeling toolbar.

label offset
The distance a label should be from the feature it labels. A label offset and a maximum label offset can be set for point features. Maximum label offsets are expressed as a percentage of the label offset. For line features, a label offset can be set from the line (similar to the label offset for point features) and along the line (which controls the position of the label relative to the ends of the line). Label offsets are not available for all label position options.

label offset constraint
The maximum distance away from a point feature that a label may be placed, beyond the specified offset.

label orientation
The angle or direction of alignment for feature labels. Labels for features are usually placed horizontally, but they may also be oriented to an angle stored as an attribute, an angle defined by the orientation of the feature geometry, or along the graticule of the data frame.

label placement option
A parameter used to define a placement property for a label. Label placement properties include such properties as label offset, label placement zone, label fitting strategy, label prioritiy, label stacking, and label weight.

label placement property
A parameter used to define a placement property for a label. Label placement properties include such properties as label offset, label placement zone, label fitting strategy, label prioritiy, label stacking, and label weight.

label placement zone
One of eight designated areas on a map, radiating from a point, in which labels may be placed. The user can indicate in which of eight zones labels should be placed, relative to the point. These preferences are taken into account when placing point labels using the Best Position placement option.

label point
In a coverage, a feature class used to represent points or identify polygons. When representing points, the x,y location of the point describes the location of the feature. When identifying polygons, the point can be located anywhere within the polygon.

Label Position tab
In Maplex for ArcGIS, a tab on the Label Placement dialog box that allows control of how labels are placed relative to features. The position of a label is determined by such parameters as: the orientation, offset, and position style for a given feature geometry.

label priority
In ArcGIS, a ranking system that determines the order in which labels will be placed on a map. Labels with higher priority will be placed before labels with lower priority. Labels placed last will have a greater chance of being crowded out or placed in an alternate position.

label rule
A parameter used to define a placement property for a label. Label placement properties include such properties as label offset, label placement zone, label fitting strategy, label prioritiy, label stacking, and label weight.

label stacking
The splitting of long labels to place the text on two or more lines. Maplex for ArcGIS allows specification of which characters trigger a split and whether or not they show up in the label.

label weight
An ESRI Standard Label Engine ranking system that indicates whether labels from a given label class may be covered by another label in cases in which label placement conflicts occur. Labels with higher weight are less likely to be overlapped than labels with lower weight.

lag
In the creation of a semivariogram, the sample distance used to group or bin pairs of points. Using an appropriate lag distance can be helpful in revealing scale-dependent spatial correlation.

LAN
Acronym for local area network. Communications hardware and software that connect computers in a small area, such as a room or a building. Computers in a LAN can share data and peripheral devices, such as printers and plotters, but do not necessarily have a link to outside computers.

land cover
The classification of land according to the vegetation or material that covers most of its surface; for example, pine forest, grassland, ice, water, or sand.

land information system
A geographic information system for cadastral and land-use mapping, typically used by local governments.

land use
The classification of land according to what activities take place on it or how humans occupy it; for example, agricultural, industrial, residential, urban, rural, or commercial.

landform
Any natural feature of the land having a characteristic shape, including major forms such as plains and mountains and minor forms such as hills and valleys.

landmark
Any prominent natural or artificial object in a landscape used to determine distance, bearing, or location.

Landsat
Multispectral, earth-orbiting satellites developed by NASA (National Aeronautics and Space Administration) that gather imagery for land-use inventory, geological and mineralogical exploration, crop and forestry assessment, and cartography.

landscape ecology
The study of spatial patterns, processes, and change across biological and cultural structures within areas encompassing multiple ecosystems.

large scale
Generally, a map scale that shows a small area on the ground at a high level of detail.

large-format printer
A printing device capable of producing an image on large paper or other media sized between 36 and 87 inches (91 and 220 centimeters) wide. Modern large format printers typically use inkjet printing technology to print an image on a roll of paper that is automatically cut to the desired length. Large-format printers may also be called plotters or wide-format printers.

LAS
An industry-standard binary file format that maintains information related to lidar data.

late binding
A COM technique that an application uses for determining an object's properties and methods at run time, rather than when the code is compiled. Late binding is generally used by scripting languages.

latitude
The angular distance, usually measured in degrees north or south of the equator. Lines of latitude are also referred to as parallels.

latitude of center
The latitude value that defines the center, and sometimes the origin, of a projection.

latitude of origin
The latitude value that defines the origin of the y-coordinate values for a projection.

latitude-longitude
A reference system used to locate positions on the earth's surface. Distances east&#8211;west are measured with lines of longitude (also called meridians), which run north&#8211;south and converge at the north and south poles. Distance measurements begin at the prime meridian and are measured positively 180 degrees to the east and negatively 180 degrees to the west. Distances north&#8211;south are measured with lines of latitude (also called parallels), which run east&#8211;west. Distance measurements begin at the equator and are measured positively 90 degrees to the north and negatively 90 degrees to the south.

lattice
A representation of a surface using an array of regularly spaced sample points (mesh points) that are referenced to a common origin and have a constant sampling distance in the x and y directions. Each mesh point contains the z-value at that location, which is referenced to a common base z-value, such as sea level. Z-values for locations between lattice mesh points can be approximated by interpolation based on neighboring mesh points.

layer
The visual representation of a geographic dataset in any digital map environment. Conceptually, a layer is a slice or stratum of the geographic reality in a particular area, and is more or less equivalent to a legend item on a paper map. On a road map, for example, roads, national parks, political boundaries, and rivers might be considered different layers.

layer file
In ArcGIS, a file with a .lyr extension that stores the path to a source dataset and other layer properties, including symbology.

layout
The arrangement of elements on a map, possibly including a title, legend, north arrow, scale bar, and geographic data.

layout view
In ArcMap and ArcReader, a view that shows the virtual page upon which geographic data and map elements, such as titles, legends, and scale bars, are placed and arranged for printing.

L-band
The group of radio frequencies that carry data from GPS satellites to GPS receivers.

LBS
Information or a physical service delivered to multiple channels, exclusively based on the determined location of a wireless device. Some location-based applications include emergency services, information services, and tracking services.

leader
In MOLE, typically two or more force elements grouped together and placed on a line based on user-specified rules. Leaders are often used to clean up the map display in cases where many symbols overlap, to group related units together, and to define perimeters or areas of interest for formations.

least convex hull
The smallest convex polygon that encloses a group of objects, such as points. In ArcGIS, TIN boundaries are convex hulls by default.

least-cost path
The path between two locations that costs the least to traverse, where cost is a function of time, distance, or some other criteria defined by the user.

least-squares adjustment
A statistical method for providing a best fit for survey point locations and detecting measurement error by minimizing the sum of the squares of measurement residuals. The method allows many measurements to participate simultaneously in a single computation.

least-squares corrections
The final measurement residuals of a least squares adjustment.

left-right topology
The topological data structure in an ArcInfo coverage that stores, for each arc, the identity of the polygons to the left and right of it. Left-right topology supports analysis functions, such as adjacency.

legend
The description of the types of features included in a map, usually displayed in the map layout. Legends often use graphics of symbols or examples of features from the map with a written description of what each symbol or graphic represents.

legend patch shape
The geometric shape of either a line or a polygon that is used to represent a specific kind of feature in a legend and in the ArcMap table of contents.

level of confidence
In a statistical test, the risk, expressed as a percentage, that the null hypothesis will be incorrectly rejected because of sampling error when the null hypothesis is true. For example, a confidence level of 95 percent means that if the same test were performed 100 times on 100 different samples, the null hypothesis would be incorrectly rejected five times.

level of detail
An abstraction of a layer in ArcGlobe portraying the layer at some degree of resolution between simplified and unsimplified.

level of significance
In statistical testing, the probability of an incorrect rejection of the null hypotheses.

leveling
In surveying, the measurement of the heights of objects and points according to a specified elevation, usually mean sea level.

LIBID
Acronym for Library Identifier. A type of GUID consisting of a unique string assigned to a type library.

library
In object-oriented programming, a logical grouping of classes, usually with a header section that lists the classes in the library.

license
The grant to a party of the right to use a software package or component. A license differs from a sale in that the user does not necessarily purchase the software but is granted the legal right to use it.

license file
A file that contains License Manager license data. Each license file contains information such as the SERVER, ESRI_SENTINEL_KEY number (Windows only), Version, the number of seats, and so on.

lidar
Acronym for light detection and ranging. A remote-sensing technique that uses lasers to measure distances to reflective surfaces.

lighting normal
In ArcScene and ArcGlobe, vectors normal to a geometry's surface, stored in that geometry to help define how lighting affects it.

limits
In Survey Analyst for field measurements, restrictions that define an acceptable level of measurement error for each computation.

line
On a map, a shape defined by a connected series of unique x,y coordinate pairs. A line may be straight or curved.

line connection
A procedure that combines groups of individual lines with the same name into a single line for the label engine. This is often necessary because lines such as roads and rivers are usually digitized as many small segments that must be connected together to represent a single real-world feature.

line event
In linear referencing, a description of a portion of a route using a from- and to-measure value. Examples of line events include pavement quality, salmon spawning grounds, bus fares, pipe widths, and traffic volumes.

line feature
A map feature that has length but not area at a given scale, such as a river on a world map or a street on a city map.

line of sight
A line drawn between two points, an origin and a target, that is compared against a surface to show whether the target is visible from the origin and, if it is not visible, where the view is obstructed.

line simplification
A generalization technique in which vertices are selectively removed from a line feature to eliminate detail while preserving the line's basic shape.

line smoothing
The process of adding extra points to lines to reduce the sharpness of angles between line segments, resulting in a smoother appearance.

lineage
A collection of states representing the changes that have occurred over time in a versioned geodatabase.

linear dimension
A measurement of the horizontal or vertical dimension of a feature. Linear dimensions may not represent the true distance between beginning and ending dimension points because they do not take angle into account as aligned dimensions do.

linear feature
A map feature that has length but not area at a given scale, such as a river on a world map or a street on a city map.

linear interpolation
The estimation of an unknown value using the linear distance between known values.

linear referencing
A method for storing geographic data by using a relative position along an already existing line feature; the ability to uniquely identify positions along lines without explicit x,y coordinates. In linear referencing, location is given in terms of a known line feature and a position, or measure, along the feature. Linear referencing is an intuitive way to associate multiple sets of attributes to portions of linear features.

linear unit
The unit of measurement on a plane or a projected coordinate system, often meters or feet.

line-on-line overlay
In linear referencing, the overlay of two line event tables to produce a single line event table. The new event table can be the logical intersection or union of the input tables.

line-on-point overlay
In linear referencing, the overlay of a line event table and a point event table to produce a single point event table. The new event table can be the logical intersection or union of the input tables.

link
In georeferencing, connections added between known points in a dataset being georeferenced and corresponding points in the dataset being used as a reference.

Link command
In Survey Analyst for field measurements, a command that finds nearby survey points for each feature vertex and automatically creates links. The command allows the user to specify the search tolerance for finding the survey points. With the Link command, users may perform batch links; it is useful to use if there are many unlinked features that need to be associated with nearby survey points.

link lines
In Survey Analyst for field measurements, lines displayed on a map after a survey point and a feature vertex are linked.

Link tool
In Survey Analyst for field measurements, a tool that allows the user to make a link between a survey point and a feature vertex by snapping and clicking a feature vertex, then snapping to and clicking the related survey point. With the Link tool, users must make each individual link manually.

LIS
A geographic information system for cadastral and land-use mapping, typically used by local governments.

List page
In Survey Analyst for field measurements, one of two types of pages in the Survey Explorer. The List page lists multiple survey objects.

little endian
A computer hardware architecture in which, within a multibyte numeric representation, the least significant byte has the lowest address and the remaining bytes are encoded in increasing order of significance.

load balance
The act of distributing application, network, and/or server resources to optimize performance.

load distribution
The act of distributing application, network, and/or server resources to optimize performance.

local analysis
The computation of an output raster where the output value at each location is a function of the input value at the same location.

local area network
Communications hardware and software that connect computers in a small area, such as a room or a building. Computers in a LAN can share data and peripheral devices, such as printers and plotters, but do not necessarily have a link to outside computers.

Local check method
In Survey Analyst for field measurements, one of two ways to apply the Coordinate Out of Tolerance command. The Local check method searches for coordinates out of tolerance within each survey project.

local datum
A horizontal geodetic datum that serves as a basis for measurements over a limited area of the earth; that has its origin at a location on the earth's surface; that uses an ellipsoid whose dimensions conform well to its region of use; and that was originally defined for land-based surveys. A local datum in this sense stands in contrast to a geocentric datum. Examples include the North American Datum of 1927 and the Australian Geodetic Datum of 1966.

local functions
The computation of an output raster where the output value at each location is a function of the input value at the same location.

local polynomial interpolation
In ArcGIS Geostatistical Analyst, a deterministic interpolation method. The interpolated surface is not required to conform to the sample data points, and the method does not have standard errors associated with it.

localization
The process of adapting software to the requirements of a different language or culture, including translating user interfaces, documentation, and help systems; customizing features; and accommodating different character sets.

location
An identifier assigned to a region or feature.

Location Aware Services
Services that allow IBM WebSphere Everywhere Access (WEA) application providers to use location-based services from multiple vendors, by providing an application programming interface (API).

location query
A statement or logical expression that selects geographic features based on location or spatial relationship. For example, a spatial query might find which points are contained within a polygon or set of polygons, find features within a specified distance of a feature, or find features that are adjacent to each other.

Location Utility Service
An OpenLS ArcWeb service used to find geographical coordinates of an address and to find an address based on the geographical coordinates (geocoding/reverse geocoding).

location-allocation
The process of finding the best locations for one or more facilities that will service a given set of points and then assigning those points to the facilities, taking into account factors such as the number of facilities available, their cost, and the maximum impedance from a facility to a point.

location-based services
Information or a physical service delivered to multiple channels, exclusively based on the determined location of a wireless device. Some location-based applications include emergency services, information services, and tracking services.

locked parcel
In Survey Analyst - Cadastral Editor, a parcel that has been locked for editing. Locked parcels cannot be edited simultaneously in a multiuser environment.

locomotion
The movements of a person following a route. Locomotion is the physical component of navigation.

log file
A database file that records changes in data, often used as part of a database restoration.

logarithm
The power to which a fixed number (the base) must be raised to equal a given number. The three most frequently used bases for logarithms are base 10, base e, and base 2.

logical expression
A string of numbers, constants, variables, operators, and functions that returns a value of true or false.

logical network
An abstract representation of a network, implemented as a collection of hidden tables. A logical network contains edge, junction, and turn elements, the connectivity between them, and the weights necessary for traversing the network. It does not contain information about the geometry or location of its elements; this information is one of the components of a network system.

logical operator
An operator used to compare logical expressions that returns a result of true or false. Examples of logical operators include less than (&lt;), greater than (&gt;), equal to (=), and not equal to (&lt;&gt;).

logical query
The process of using mathematical expressions to select features from a geographic layer based on their attributes; for example, "select all polygons with an area greater than 16,000 units" or "select all street segments named Green Apple Run."

logical selection
The process of using mathematical expressions to select features from a geographic layer based on their attributes; for example, "select all polygons with an area greater than 16,000 units" or "select all street segments named Green Apple Run."

long transaction
An edit session on a feature dataset that may last from a few minutes to several months. Long transactions are managed by the ArcSDE versioning mechanism.

longitude
The angular distance, usually expressed in degrees, minutes, and seconds, of the location of a point on the earth's surface east or west of an arbitrarily defined meridian (usually the Greenwich prime meridian). All lines of longitude are great circles that intersect the equator and pass through the North and South Poles.

longitude of center
The longitude value that defines the center, and sometimes the origin, of a projection.

longitude of origin
The longitude value that defines the origin of the x-coordinate values for a projection.

long-range variation
In a spatial model, coarse-scale variation that is usually modeled as the trend.

loop traverse
In surveying, a traverse that starts and ends with the same survey point.

loose coupling
A relatively unstructured relationship between two software components or programs that work together to process data, which requires little overlap between methods, ontologies, class definitions, and so on.

loosely coupled replication
A replication model that does not require the parent and child replicas to be directly connected for synchronization to occur. Loosely coupled replication is an asynchronous model, so edits made in one replica have no effect on other related replicas until synchronization. Synchronization can be executed manually, or it can be automated.

lossless compression
Data compression that has the ability to store data without changing any of the values, but is only able to compress the data at a low ratio (typically 2:1 or 3:1). In GIS, lossless compression is often used to compress raster data when the pixel values of the raster will be used for analysis or deriving other data products.

lossy compression
Data compression that provides high compression ratios (for example 10:1 to 100:1), but does not retain all the information in the data. In GIS, lossy compression is used to compress raster datasets that will be used as background images, but is not suitable for raster datasets used for analysis or deriving other data products.

low-level language
A programming language that uses keywords and statements that are little more complex than the ones and zeros of machine language. Low-level language technically includes machine language, but more commonly refers to an assembly language that uses symbols to make machine instructions easier for programmers to read and understand. Each statement in assembly language represents a single command to the processor, affording the developer only a low level of abstraction in regard to mundane functions such as memory access and register storage, meaning such operations demand the developer's close attention.

low-pass filter
A spatial filter that blocks high-frequency (shortwave) radiation, resulting in a smoother image.

loxodrome
A complex curve on the earth's surface that crosses every meridian at the same oblique angle. A rhumb line path follows a single compass bearing; it is a straight line on a Mercator projection, or a logarithmic spiral on a polar projection. A rhumb line is not the shortest distance between two points on a sphere.