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92 Cards in this Set
- Front
- Back
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definition of GIS
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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. |
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describe Vector systems
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x,y coordinates are used to describe features as points,
lines, and areas. Attribute data are stored in a related data table. |
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What kind of data are best represented by vector systems?
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discrete data.
(vs continuous) |
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describe Raster systems
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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 |
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What kind of data are best represented by raster systems?
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image format and continuous data
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A feature defined by a single x,y coordinate,
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point
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A feature represented by a chain of x,y
coordinates, |
line, arc
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A feature represented by a closed
series of set of lines. |
area, polygon
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A feature that represents a 3-D surface,
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Volume: TIN (triangulated irregular network)
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Composite areas that have disjoint or overlapping objects
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region
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Describe "discrete" data
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have a defined
geographic extent. Distinguishable features with defined geometry. |
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define continuous data
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ave a spatially
variable geographic extent. Features are transitional over their geometry. |
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categorical data (e.g.,
landuse) is defined on what kind of scale? |
nominal scale
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ranked or ordered data (e.g.,
hazard class)is defined on what kind of scale? |
ordinal scale
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quantified data with a
relative zero (e.g., temperature) is classified on what kind of scale? |
interval scale
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quantified data with an absolute
zero (e.g., income) is categorized on what kind of scale? |
ratio scale
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what are attribute data?
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Attribute data are variables (data)
that describe a geographic feature (the population of Kenya, the area of a watershed, etc.) |
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What are spatial data, as opposed to attribute data?
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points, lines, areas or volumes
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describe a georelational model
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feature based data
model that stores data as spatial and linked attribute data in layers. |
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What is a geodatabase model (hint: this differs from a georelational model)
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an object based data
model that organize spatial data, properties, and methods that define the characteristics and behaviors of spatial objects. |
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define a layer
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internally consistent logical set of
features and attributes aka THEME or COVERAGE (esri products) |
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what's a shapefile?
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Shapefiles are a simple, non-topological
format for storing the geometric location and attribute information of geographic features. |
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What is a coverage?
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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 |
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topological classes:
topographical identification of adjacent POLYGONS by recording the left and right polygons of each arc. |
contiguity
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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.
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connectivity
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what are 5 topological classes?
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Connectivity (connecting arcs)
Contiguity (or adjacencies, left and right polygons) Area definitions (built from bounding arcs) Regions Routes |
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why implement underscore use?
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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. |
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What is UTM?
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Acronym for universal transverse Mercator. A projected coordinate system that divides the world into 60 north and south zones, 6 degrees wide.
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What is stateplane?
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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
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What is Lat/Long?
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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.
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what is a coordinate system?
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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 |
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What is a TIC point?
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(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. |
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Projection which maintains angles and shapes at points
(local) |
Conformal
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What is a GCP?
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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" |
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Projection which maintains area
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equal area
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A projection that does not have equal area, conformal, or equidistant characteristics
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compromise
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what is a standard line?
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A line on a sphere or spheroid that has no length compression or expansion after being projected; usually a standard parallel or central meridian.
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principal meridian?
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the principal north-south line used for survey control in a large region. Divides between east and west
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what is a datum?
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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.
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examples of datums?
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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 |
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projection that retains direction?
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azimuthal
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____________ are not
acceptable for display and analysis! They are good for data management. _____ is needed for display & analysis. |
Geographic coordinate systems
A projection |
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How can Geographic coordinates be expressed?
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DMS: degrees minutes seconds
DD: Decimal Degrees |
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___________ is a location
reference system (latitude and longitude) for spatial features on the surface of the Earth. |
Geographic coordinates
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explain scale factor.
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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.
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what are projection files? prj.
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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. |
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what is on-the-fly projecting?
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when additional layers are added to a map, they are projected on the fly to match the first projection.
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What is a georelational model?
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A GIS data models
that stores spatial & attribute data in two separate related data bases using a relational data base. |
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What is topology?
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In geodatabases, the arrangement that constrains how point, line, and polygon features share geometry.
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What is a region?
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Coverage type: a geographic area with similar characteristics
may be joint, disjoint, or overlapping. multiple polygons shape a region, but all with same attributes. |
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Geodatabase
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aka: object based data model. Stores data as objects. Spatial data and attributes
are stored in one record for each object. |
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examples of data models vs data structures?
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Structures: shp. , gdb.
Models: Raster, vector |
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cell values?
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the class, category, group, magnitude, distance or relationship assigned to a raster cell
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Cell size?
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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 |
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what encodes grid size and locational
information? |
reference world files
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reference world file
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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. |
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What is run length encoding?
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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. |
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Attribute types:
short integer |
Short Integer – one sign bit and 2^15 values (±32,000)
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Attribute types:
long integer |
Long Integer – one sign bit and 2^31 values (±2 bil.)
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Attribute types:
floating |
Floating – one sign, 7 exponent, and 24 mantissa bits
1.2345 x 10^2 |
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Attribute types:
double |
one sign, 7 exponent, and 56 mantissa bits
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Attribute types:
text |
(8 bit) character string – text values
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Attribute types:
date |
date in standard time format
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Attribute types:
blob |
multimedia content objects
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What is bit depth?
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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 |
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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) |
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Sources of GIS Data:
Private or Proprietary Data |
data
developed by private industry or valueadded data for profit (e.g., ESRI and TransCAD data) |
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What is metadata?
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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. |
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Arc?
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string of coordinates that define a
linear feature or an edge of a polygon |
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Node?
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end points and intersections of
arcs |
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Vertex?
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intermediate points along a
line that represent changes in a lines pathway (Nodes are only intersections and end points) |
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What is a label point?
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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.
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line- generalization?
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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 |
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line smoothing?
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process of using a mathematical
function to define a smooth least curvature line for a set of points. makes it look nice after generalization. |
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fuzzy tolerance?
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the minimum distance
between VERTICES and ARCS due to imprecision or digitizing errors |
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in editing: a line that extends past its intended location?
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overshoot
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What is undershoot (in editing)?
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gap between a node and the
line it should connect to, may create unclosed polygons. |
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spurious polygons that
result from mismatches in coincident boundary lines are called...? |
splinter polygons
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edgematching?
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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) |
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conflation??
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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. |
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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
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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
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common errors in labeling?
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missing, multiple or duplicate labels.
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2 main types of errors in editing?
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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. |
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Macro level components:
Lineage |
A collection of states representing the changes that have occurred over time in a versioned geodatabase.
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RMS error
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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.
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What are the important MACRO components that effect data quality?
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Completeness, time, lineage
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What are the important MICRO components that effect data quality?
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positional and attribute accuracy
resolution logical consistency conflation (resolved location errors) |
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Why manage error rather than eliminate it?
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sources may have errors- data is tied together, complex.
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What is weed tolerance? (weed distance)
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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.
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Snap distance?
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the minimum distance
between two NODES or points to be considered the same location (weed is for vertices only) |
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digitizing?
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The process of converting the geographic features on an analog map into digital format
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