Bolstad-Gis Fundamentals Ch.4

The process of taking coordinates from a map, image or other source and converting them to a digital format in a GIS.

An electronic depiction of spatial data.

Map component that contains most of the depicted spatial data. Usually the largest component.

Included to provide a frame around all map elements.

The ratio of the distance on the map to corresponding distance on the ground.

Maps in which coordinate lines represent constant latitude and longitude.

Coordinate lines of latitude and longitude may appear curved depending on Map Scale, the map coordinate system, and the location of the area on the Earth's surface.

Map depiction of lines of constant coordinates.

Graticules are useful in depicting distortion in a map because they show how the geographic North or East lines are deformed and how this distortion varies across the map.

Grids may establish a map-projected north, and may be useful when trying to navigate or locate a position on a map.

A faithful representation of the relative position of objects. Suitable source of spatial data.

Map of points, lines or areas.

Map depicting the quantitative information for areas. Each area is given a color, shading or pattern corresponding to values for a mapped variable.

Commonly used to show quantitative data, dots are placed in a polygon or area such that the number of dots equals the total value for that polygon. Dots are typically placed randomly within the polygon area.

Map representing continuous surfaces such as rainfall, elevation or temperature.

Depictions of cliffs or overhangs in a contour map of elevation' may have lines that coincide when there is a common positional value.

The approximation of real features when they are represented on a map due to the impossibility of collecting every geometric or attribute detail of the physical world.

The modification of features when representing them on a map.

Fused - multiple features may be grouped together to form a larger feature.

Simplified - boundary or shape details are lost or "rounded off".

Displaced - features may be offset to prevent overlap or to provide a standard distance between mapping symbols.

Omitted - small features may be excluded.

Exaggerated - standard symbol sizes may be larger when scaled to the true width of the feature.

Exaggerated - standard symbol sizes may be larger when scaled to the true width of the feature.

When map generalization results in omission or degradation beyond acceptable levels.

The conversion of digitizer or other coordinate data to an Earth surface coordinate system.

The human-guided coordinate capture from a map or image source.

On-screen and hardcopy.

Manual digitization occurs in a computer screen using a digital image as a backdrop.

Human guided coordinate capture from a paper, plastic or other hardcopy map using an electrically sensitized pick to trace lines or points on a map that is secured to a digitizing surface.

The operator must depress a button or in some way signal to the co outer to sample each point.

Points a automatically sampled at fixed time or distance frequency.

A variant of stream mode digitizing where a new point is not recorded unless it is more than some minimum threshold distance from a previously sampled point.

Nodes that do not quite reach a line or another node, causing unconnected networks and included polygons.

May not cause problems in defining polygons but may cause problems when defining and analyzing line networks.

A set of polynomial functions that join smoothly. Used to smoothly interpolate curves between digitized points.

A scanner passes a sensing element over an illuminated map. The sensor measures the location of a point and the strength of light reflected from the point. These intensities are converted into numbers.

Reducing the widths of lines or points to a single pixel. Often required in scan digitization, especially when the data are to be converted into vector format.

Bringing spatial data into an Earth-based coordinate system to ensure that each data layer aligns with every other data layer.

Used to transform digitized data from the digitizer coordinate system to a map-projected coordinate system. The locations of control points are known in the map projection coordinates and the digitizer coordinates.

Reassigning cell values when changing raster coordinates or geometry.

Taking the output value from the nearest input layer cell center.

Distance-based averaging of the four nearest cells.

A weighted average of the 16 nearest cells.

Typically employs a statistically-fit linear equation to convert coordinates from one Cartesian coordinate system to another.

An analytical, formula-based conversion between coordinate systems, usually from a curved, latitude/longitude coordinate system to a Cartesian coordinate system.

No statistical fitting process is used with a map projection.

Spatial Data Transfer Standard

1- a logical specification

2- a description of the types of features supported

3- the ISO encoding used

Information about spatial data including content, source, lineage, developer, coordinate system, extent, structure, spatial accuracy, attributes, and responsible organization for spatial data.