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92 Cards in this Set

  • Front
  • Back
definition of GIS
Systems of hardware, software, data,
people, organizations, and institutional
arrangements for collecting, storing,
analyzing, and displaying of information
about areas of the earth.

Another definition:
computer system for the capture,
storage, query, analysis
and display of
geographically referenced
data.
describe Vector systems
x,y coordinates are used to describe features as points,
lines, and areas. Attribute data are stored in a
related data table.
What kind of data are best represented by vector systems?
discrete data.
(vs continuous)
describe Raster systems
Raster systems or grid – cell based systems record
attributes at locations, a mesh of unit-area cells.
Attributes stored as CELL values or key values
What kind of data are best represented by raster systems?
image format and continuous data
A feature defined by a single x,y coordinate,
point
A feature represented by a chain of x,y
coordinates,
line, arc
A feature represented by a closed
series of set of lines.
area, polygon
A feature that represents a 3-D surface,
Volume: TIN (triangulated irregular network)
Composite areas that have disjoint or overlapping objects
region
Describe "discrete" data
have a defined
geographic extent. Distinguishable features
with defined geometry.
define continuous data
ave a spatially
variable geographic extent. Features are
transitional over their geometry.
categorical data (e.g.,
landuse) is defined on what kind of scale?
nominal scale
ranked or ordered data (e.g.,
hazard class)is defined on what kind of scale?
ordinal scale
quantified data with a
relative zero (e.g., temperature) is classified on what kind of scale?
interval scale
quantified data with an absolute
zero (e.g., income) is categorized on what kind of scale?
ratio scale
what are attribute data?
Attribute data are variables (data)
that describe a geographic
feature (the population of Kenya,
the area of a watershed, etc.)
What are spatial data, as opposed to attribute data?
points, lines, areas or volumes
describe a georelational model
feature based data
model that stores data as spatial and linked
attribute data in layers.
What is a geodatabase model (hint: this differs from a georelational model)
an object based data
model that organize spatial data, properties,
and methods that define the characteristics
and behaviors of spatial objects.
define a layer
internally consistent logical set of
features and attributes

aka THEME or COVERAGE (esri products)
what's a shapefile?
Shapefiles are a simple, non-topological
format for storing the geometric location
and attribute information of geographic
features.
What is a coverage?
A topological vector data format used in
ESRI products. Originally developed for
use with ESRI’s Arc/Info applications.
Allows for the storage of a related set of
points, lines, and/or areas within a folder.
Note: attribute data a stored in a linked
“Info” folder
topological classes:
topographical identification of adjacent POLYGONS by recording the left and right polygons of each arc.
contiguity
topological classes:topological identification of connected ARCS by recording the from-node and to-node for each arc. Arcs that share a common node are connected.
connectivity
what are 5 topological classes?
Connectivity (connecting arcs)
Contiguity (or adjacencies, left and right polygons)
Area definitions (built from bounding arcs)
Regions
Routes
why implement underscore use?
in command line systems such as
ArcInfo spaces indicate separators between
parameters. File names with spaces put the
parameters out of order which is a very bad thing.
What is UTM?
Acronym for universal transverse Mercator. A projected coordinate system that divides the world into 60 north and south zones, 6 degrees wide.
What is stateplane?
A group of planar coordinate systems based on the division of the United States into more than 130 zones to minimize distortion caused by map projections. Each zone has its own map projection and parameters and uses either the NAD27 or NAD83 horizontal datum. The Lambert conformal conic projection is used for states that extend mostly east–west, while transverse Mercator is used for those that extend mostly north–south. The oblique Mercator projection is used for the panhandle of Alaska
What is Lat/Long?
A reference system used to locate positions on the earth's surface. Distances east–west are measured with lines of longitude (also called meridians), which run north–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–south are measured with lines of latitude (also called parallels), which run east–west. Distance measurements begin at the equator and are measured positively 90 degrees to the north and negatively 90 degrees to the south.
what is a coordinate system?
A reference framework consisting of a set of points, lines, and/or surfaces, and a set of rules, used to define the positions of points in space in either two or three dimensions.
Eg. lat/long or UTM
What is a TIC point?
(4 points we used on zoning image)

"known latitude longitude in
MAP TO MAP transformations"

A geographic control point for a coverage representing a known location on the earth's surface. Tics allow all coverage features to be recorded in a common coordinate system. Tics are used to register map sheets when they are mounted on a digitizer. They are also used to transform the coordinates of a coverage, for example, from digitizer units (inches) to the appropriate values for a particular coordinate system.
Projection which maintains angles and shapes at points
(local)
Conformal
What is a GCP?
Ground control point:
A system of points with known positions, elevations, or both, used as fixed references in georeferencing maps

"image to real-world coordinate transformations"
Projection which maintains area
equal area
A projection that does not have equal area, conformal, or equidistant characteristics
compromise
what is a standard line?
A line on a sphere or spheroid that has no length compression or expansion after being projected; usually a standard parallel or central meridian.
principal meridian?
the principal north-south line used for survey control in a large region. Divides between east and west
what is a datum?
a set of reference points on the Earth's surface against which position measurements are made & an associated model of the shape of the Earth to define a geographic coordinate system.
examples of datums?
NAD 27 – North American Datum 1927
NAD 83 – North American Datum 1983 (more accurate that 27!)
GRS 83 – Geodetic Reference System (world)
WGS 84 – World Geodetic Survey 1984
HARN – High Accuracy Reference Network
projection that retains direction?
azimuthal
____________ are not
acceptable for display and analysis! They
are good for data management. _____ is needed for display & analysis.
Geographic coordinate systems

A projection
How can Geographic coordinates be expressed?
DMS: degrees minutes seconds
DD: Decimal Degrees
___________ is a location
reference system (latitude and longitude) for
spatial features on the surface of the Earth.
Geographic coordinates
explain scale factor.
The reciprocal of the ratio used to specify scale on a map. For example, if the scale of a map is given as 1:50,000, the scale factor is 50,000.
what are projection files? prj.
used to store the
coordinate information for a given geographic
data set. These allow for data to be displayed
properly and allow for the projection from one
coordinate space to another coordinate space.
Furthermore, they allow for on-the-fly projection
to function in ArcGIS.
what is on-the-fly projecting?
when additional layers are added to a map, they are projected on the fly to match the first projection.
What is a georelational model?
A GIS data models
that stores spatial & attribute data in two
separate related data bases using a relational data
base.
What is topology?
In geodatabases, the arrangement that constrains how point, line, and polygon features share geometry.
What is a region?
Coverage type: a geographic area with similar characteristics
may be joint, disjoint, or overlapping.

multiple polygons shape a region, but all with same attributes.
Geodatabase
aka: object based data model. Stores data as objects. Spatial data and attributes
are stored in one record for each object.
examples of data models vs data structures?
Structures: shp. , gdb.

Models: Raster, vector
cell values?
the class, category, group, magnitude, distance or relationship assigned to a raster cell
Cell size?
The dimensions on the ground of a single cell in a raster, measured in map units. Cell size is often used synonymously with pixel size.
eg. cell = pixel = 40 feet
what encodes grid size and locational
information?
reference world files
reference world file
encode grid size and locational
information.
aka: header file

A text file containing information about where an image should be displayed in real-world coordinates.
What is run length encoding?
the compression of raster files- compresses 1's and 0's

If two or more adjacent cells in a row have the same value, the database stores that value once instead of recording a separate value for each cell.
Attribute types:
short integer
Short Integer – one sign bit and 2^15 values (±32,000)
Attribute types:
long integer
Long Integer – one sign bit and 2^31 values (±2 bil.)
Attribute types:
floating
Floating – one sign, 7 exponent, and 24 mantissa bits
1.2345 x 10^2
Attribute types:
double
one sign, 7 exponent, and 56 mantissa bits
Attribute types:
text
(8 bit) character string – text values
Attribute types:
date
date in standard time format
Attribute types:
blob
multimedia content objects
What is bit depth?
Bit Depth determines the range of values or
categories that can be encoded, 2^nth
1 bit = 2^1 0 – 1(Binary) eg: fax- on/off
8 bit = 2^8 0 – 255 eg: grayscale, 255 shades
16 bit = 2^16 0 – 65,535
24 bit = 2^24 0 - 16,777,215 RGB- 16 mill different colors
Sources of GIS Data:
Public Domain Data
data that belong to
the public as a whole and not subject to
copyright (e.g., USDA and USGS data)
Sources of GIS Data:
Private or Proprietary Data
data
developed by private industry or valueadded
data for profit (e.g., ESRI and
TransCAD data)
What is metadata?
provide information about geospatial data

a. data on area covered, units, projection,
features, attributes, data quality, and data
currency (time).
b. provides information on data transfer, data
formats, processing, citations, etc.
Arc?
string of coordinates that define a
linear feature or an edge of a polygon
Node?
end points and intersections of
arcs
Vertex?
intermediate points along a
line that represent changes in a lines pathway

(Nodes are only intersections and end points)
What is a 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.
line- generalization?
the process of
simplifying a line by removing some points,
commonly used for reducing the scale of a
dataset to avoid jumbling of the line
line smoothing?
process of using a mathematical
function to define a smooth least curvature
line for a set of points. makes it look nice after generalization.
fuzzy tolerance?
the minimum distance
between VERTICES and ARCS due to imprecision
or digitizing errors
in editing: a line that extends past its intended location?
overshoot
What is undershoot (in editing)?
gap between a node and the
line it should connect to, may create unclosed
polygons.
spurious polygons that
result from mismatches in coincident
boundary lines are called...?
splinter polygons
edgematching?
process of matching lines
along the edge of adjacent data layers (tiles)
across the border
Typically, one layer is defined as a master and
the other a slave – slave is matched to the
master layer (not a very happy choice of
words for this)
conflation??
the process of resolving location
errors between layers of data that have
features that should align
For example, ensuring that lines that represent
county lines align with the incorporated and
unincorporated boundaries that are coincident.
What is a node that does not
connect two arcs together. It may represent a
legitimate feature, e.g., starts of tributaries or
dead-end streets
dangling node
What is a node that breaks a
continuous line into separate lines, some
pseudo nodes are acceptable where the
attributes of a line may change attributes
pseudo-node
common errors in labeling?
missing, multiple or duplicate labels.
2 main types of errors in editing?
Location & digitizing. (accuracy & precision)

Location Errors – are errors in the geometric
position of features

Digitizing – process of converting an analog
to digital format – vector entry of xy
coordinates that represent a feature or the
raster scan of an image.
Macro level components:
Lineage
A collection of states representing the changes that have occurred over time in a versioned geodatabase.
RMS error
Acronym for root mean square error. A measure of the difference between locations that are known and locations that have been interpolated or digitized. RMS error is derived by squaring the differences between known and unknown points, adding those together, dividing that by the number of test points, and then taking the square root of that result.
What are the important MACRO components that effect data quality?
Completeness, time, lineage
What are the important MICRO components that effect data quality?
positional and attribute accuracy
resolution
logical consistency
conflation (resolved location errors)
Why manage error rather than eliminate it?
sources may have errors- data is tied together, complex.
What is weed tolerance? (weed distance)
The minimum distance allowed between any two vertices along a line, set before digitizing. When new lines are added, vertices that fall within that distance of the last vertex are ignored. Weed tolerance applies ONLY TO VERTICES, not to nodes.
Snap distance?
the minimum distance
between two NODES or points to be considered
the same location
(weed is for vertices only)
digitizing?
The process of converting the geographic features on an analog map into digital format