Glossary - Spatial Mathematics: Theory and Practice through Mapping - page 240

Buffers 35, Analysis 35, Local 35, Direction 35, Length 34, Place 34, Polygons
34, Function 34.
Knowledge, however, may (in part) feed the imagination. To that end, we
offer a set of terms and definitions or comments about them. Some are techni-
cal, others are common words used with perhaps uncommon meaning within
this context. The word cloud for the entire book selects words based only on
frequency. In contrast, in this glossary the authors select approximately ten
words or short phrases from each of the 10 chapters and offer brief explana-
tory material about each of them.
Absolute location: Exact location designated using a recognized coordinate
system.
Accuracy: A measure of whether points taken in a system are close to an
accepted value.
Antipodal points: Points at opposite ends of a diameter of a sphere.
Aspect ratio: Ratio of horizontal dimension to vertical dimension (or
vice-versa).
Attribute table: In a GIS, a table of data linked to a map containing charac-
teristics of the data being mapped.
Azimuthal: In mapping, the projection of the surface of the globe to a plane.
Bar scale: A graphical way of expressing map scale that changes with
enlargement and reduction of the map.
Base map: The first layer of a map; a map to build from. Often a simple
outline map. A GIS, often refers to the raster layer such as imagery or
topography that is typically streamed online.
Blocks: A statistical area for Census purposes typically bounded by city
streets or some other physical feature. Blocks are aggregated into
Block groups; blocks are usually synonymous in urban areas to city
blocks.
Block groups: A cluster of blocks that serves as a statistical collection unit
for US Census data.
Buffer: In a GIS, the zone around a map feature measured in units of time or
distance; used in proximity analysis.
Cartesian coordinate system: Specifies any given point in the plane uniquely
by a pair of numerical coordinates which are signed distances from
the point to two fixed perpendicular lines that intersect at the origin;
named for René Descartes.
Central tendency: A single summary measure for one variable—an average.
Choropleth map: A thematic map with areas shaded in proportion to the
measurement of the variable being mapped.
Classification: In mapping, the partitioning of data according to various sys-
tematic methods. Quantile, natural breaks, geometrical interval, equal
interval, standard deviation are common methods.
Close-packing: Packed tightly together; compactly arranged.
Cluster: Grouping of data.