First Test Oct 6 Flashcards
GIS refers to?
the hardware and software required to store spatial coordinate information for features called attributes
GIS data format is a …
collection of data points, lines, and polygons
annotation
text/labels on maps
choropleth maps
use light to dark shades of a particular color to indicate the relative number of a quantitative feature
dot density map
point data that is interpolated to create a continuous map coverage
continuous data
aka rastor data. a quantity that exists over the entire map area; always present; changes in value from place to place - elevation, precipitation, temperature; represent a measurement that occurs everywhere; thousands or millions of potential values; few adjacent cells have same values
vector model
features are stored as a series of X-Y coordinates in a rectangular coordinate system.
features can have ___ geometry shapes
3; points, lines, and polygons
feature class
collection of similar objects with the same attributes, stored as a single unit
a small scale map :
large denominator shows a large area
a large scale map
small demonintaor shows small areas
it is important to distinguish between ? and ?
source scale and map scale
precision
number of sig figs in a measurement
metadata
contains information about data that people need to understand the data and evaluate its quality. should be provided with every data set distributed to the public; advised for in-house data as well
topology
describes the spatial relationships between features - adjacency, connectivity, overlap, and intersection
logical consistency
describes how well the features mimic the real world situations; usually confined to testing for topology errors
RGB color model
each primary color brightness is indicated on a scale of 0 (black) to 255 (light)
HSV color model
hue represents the color on a scale of a 0-360 (color wheel); saturation represents the intensity of the color (0-100); value represents the brightness of the color (0-100)
CMYK color model
is considered to be a “subtractive” model as the colors are removed from white light
categorical data
may be text or numeric, portrayed with a unique values map
ordinal data
is a type of categorical data based on either quantitative or qualitative data; use a unique values map with a single hue color scheme
ratio data
places values along a regular scale with a meaningful zero point
interval and ratio data must
be divided into classes before mapping
quantities data
are mapped using variations in symbol size, thickness, and hue
quantile classification
puts the same number of features in each class - best used when data is uniformly distributed
standard deviation classification
compares values close to and far from from the mean - best used when data is normally distributed as a bell curve
geometrical interval classification
multiples each class range by a constant - best for visualizing strongly skewed or logarithmically increasing data
minimizing Modifiable Areal Unit Problem
normalizing (dividing) data by a suitable field allows data patterns to emerge
visual Modifiable Areal Unit Problem
large polygons dominate map
layer files
easy way to transfer the same symbology to multiple maps of projects
otyles
set of symbols stored together; viewed and selected on symbology pane
discrete data
objects such as roads or land use polygon; take on relatively few values; adjacent cells often have same values; values may change abruptly at boundaries
five steps of map design
select, arrange, symbolize, review and edit
visual center of a page is about…
5% higher than the geometric center
elements of a map
data frames, title, dynamic text: spatial reference, text scale, RF scale; inserted text, north arrow, scale bar, legend, grid lines, neat lines
map grids
longitude and latitude marks around the map frame, show x-y coordinates, index grids show
desirable map properties
conformal (shapes accurate); equal area ( areas correct ); equidistant ( distances accurate); azimuthal (directions accurate)
no map projection can…
preserve both correct area values and accurate shape of features; can’t have conformal and equilibrium at same times
unprojected geographic coordinate system
based on spherical globe coordinates; degrees of latitude and longtitude
projected coordinate system (PCS)
converts spherical coordinates to planar, set of math equations, projects 3D coordinates to 2D map
geoid
is defined by gravity measurements that have the same value everywhere
ellipsoid (spheroid) represents..
local reference for elevation ellipsoid is defined by length of axis: major and minor axis that represent longer and shorter radii of ellipsoid
datum
to minimize the discrepancy between the geoid and ellipsoid a datum is defined; shifts the ellipsoid relative to the geoid to achieve a best fit between the two
local datum
optimizes the shift for the best fit at a particular location; optimized for a country or continent or local area
geocentric or world centered datum..
optimizes the fit for the entire earth
datum transformations
converting one datum to another requires specialized fitting - several methods available; converting datums should be done only when necessary
types of geometric projections
cylindrical, conic, azimuthal
projection parameters
a projection is customized to work for the map region by setting parameters; central meridian, standard parallels, latitude of origin; false easting and north easting
standard parallels
occur where the projection surface touches the ellipsoid; a tangent projection has one standard parallel; a secant projection has two standard parallels; parallels are lines of no distortion
false easting and northing:
arbitrary values added to x and y values ensures that all coordinate numbers are positive
state plane projection system
states divided into one or more zones identified by a unique FIPS ( Federal information processing standard)
