GIS CONCEPTS AND TERMINOLOGY
Maps are graphic representations of the real world. Only a general representation because
we all know that the real world is too detailed to be replicated. Real world comprised of
objects (real and man-made). Maps comprised of features that represent real world
objects. Features comprised of attributes (i.e. feature = river; attribute = name, length,
avg. depth)
 Features – a map representation of a geographic object (church, school, river, lake, forest)
 Each map feature has a location, shape, symbol
1) Locations – map representation of where a particular object is in relation to other
objects (because earth is sphere and maps are flat, there is always distortion of
location of features on maps – discuss later – projections)
2) Shape – visible form of a geographic object. In arcview, shape is the the technical
name for a map feature, stored in a shapefile format. (maps use 3 basic shapes to
represent real world objects (points, lines, polygons)
a. Points – represent objects that have discrete locations and are too small
to be depicted as polygons
b. Lines – represent objects that have length but are too narrow to be
depicted as polygons
c. Polygons- represent objects too large to be depicted as points or lines
3) Symbols – particular graphic element (defined by some combination of shape,
size, color, angle, outline, or fill pattern) used to draw a feature. Symbols identify
map features
a. There are symbols for points (school, airplane, book), lines (thick, thin,
solid or broken), and polygons (colors & patterns)
 Text Labels – identify map features (often used in conjunction with symbols)
 Scale – relationship b /w dimensions of features on a map and the geographic objects
they represent on the earth (i.e. scale of 1:100,000 means one unit of measure on the map
equals 100,000 of the same unit on the earth)
1. What happens to map features when you increase map scale? What about
when you decrease scale? See movement from polygon/area to a point and
vice versa
 Table – data structure that stores features' attributes in rows and columns. Also known
as an attribute table or themes, ArcView can read tables in dBase, Info, Fpro, Text. GIS
stores attribute info about map features in tables (database
1. Attribute Tables formatted by rows and columns
2. Each column stores different attributes
3. Each row relates to a single feature
 Theme – Link features with their attributes. Set of geographic features of the same type,
along with their attributes (i.e. monthly burglaries, Orange County Banks, street lights)
 Shapefile – ArcView’s format for storing location, shape, and attribute information of
geographic features
 TIGER – acronym for Topologically Integrated Geographic Encoding and Referencing.
A data format used by the US Census Bureau to store street address ranges and census
tract/block boundaries (basis for all base maps).
 X axis – planar coordinate system, horizontal axis representing east/west
 Y axis – planar coordinate system, vertical axis representing north/south
 X,Y Coordinates – Values representing the location of a point in a plane, relative to the
axes of its coordinate system.
 Link b/w map features and attributes basic principle behind how GIS works
1) Once map features and attributes are linked, you can access the attributes for any map
feature or locate any feature from its attributes in a table (EX 7a)
2) Link b/w features and attributes is dynamic
a. Can access either one by accessing the other
b. Changing an attribute in the table automatically changes it on the map (i.e. if
change one street from 2 to 6 lane, and these have different symbols, the
changed street will automatically receive a 6 lane symbol)