CP 4510 GIS Exam

Types of Projections

1. Cylindrical (preserve direction and shape) 2. Conic (preserve area and/or distance) 3. Azimuthal or planar (preserve area and/or distance)

Ways to classify numeric data

1. Natural Breaks 2. Equal Interval 3. Standard Deviation 4. Quantiles 5. Geometric Intervals

Types of Thematic Maps

1. Unique value 2. Graduated Colors (polygons) 3. Graduated Symbol (Points) 4. Dot Density 5. Chart Maps

4 differences in Vector vs. Raster Model

1. Vector is discrete/categorical data while Raster is continuous data 2. Vector is integer values while Raster is floats or ints. 3. Vector has only value per category and Raster has large range in values. 4. With raster it is unlikely to have same values as adjacent cells

all map projections have one or more of these 4 distortions

1. direction 2. shape 3. area 4. distance

Ellipsoids

Actual shape of the earth. smooth shape with slightly smaller n/s axis.

Geographic (unprojected) Coordinate System

Based on spherical coordinates. Measured in degrees of lat and long

Projected Coordinate System

Converts spherical coordinates to planar coordinates. Uses set of mathematical equations and projects 3d coordinates to 2d map.

Discrete vs Continuous Map Data

Discrete: objects exist in defined location (Point, lines, polygons) Continuous: Data exist everywhere (raster)

Defined or Equal Interval

Equal Sized classes. User chooses class range for defined interval map or number of classes for equal interval map.

Categorical Data

Features belong to categories (rock type, volcano type, etc.). Portrayed with unique values map, and categories can be numeric or text.

Natural Breaks

Jenks Optimization method and exploits natural gaps in data. Good for skewed data

MAUP

Modifiable Area Unit Problem: maps reflect the influence rather than data being mapped

Common Geograhpic Coordinate System for US

NAD 1983

Common Projected Coordinate System for US

North American Equisdistant Conic

Interval Data

Places values along a regular numeric scale (elevation). can have negative values. Examples are temperature, population change

Ratio Data

Places values along regular scale with meaningful zero point and no negative values. Population of state capitals

Map Scale

Ratio of distance on map to distance on the ground. Dimensionless. 1 cm on map= 100,000 cm on ground

Common Projected Coordinate System for local areas

State Plane and UTM's

Ordinal Data

Type of categorical data: Ranks categories using along a scale and uses a unique values map

Vector model

best for discrete data. features are stored map objects (points, lines, polygons) 1 to 1 relationship between feature and row in table

Standard Deviation

compares values close to and far from the mean. (<0.5 std dev or 0.5-1.0 std devs)

Define Projection Tool vs Project Tool

define projection: 1. creates or changes only the CS Label 2. does not change coordinates in the file 3. Keeps original data set 4. use only when CS is missing or incorrect Project: 1. Changes coordinates in the file 2. Changes the label 3. Creates new data set 4. Use when changing a CS permanently. 5. used to assemble collections of data with the same stored CS.

Normalizing by Field Percentage

dividing each value by the total of all values. (Number of congressional districts in each state by total # of districts to get percentage of congress in each state)

Raster Model

geographic space quantized into uniformly sized discrete units called pixels. Each pixel contains a numeric value that can be an int or float.

projection

mathematical conversion of points on the earth's surface to flat plane (map)

Geometrical Interval

multiplies each class range by a constant, best for visualizing strongly skewed or log increasing data like population density

Nominal Data

names or uniquely identifies objects. (Country Names, capital cities, rivers, water bodies). usually portrayed on single symbol map

Quantile

same number of features in each class (Linear data distribution)

Geoid

surface modeled from gravity differences and is closest to true shape but too complicated for mapping.

Datum

to minimize discrepancy between geoid and ellipsoid these are used. datum shifts the ellipsoid relative to the geoid to achieve best fit. a geocentric or world centered datum optimizes fit for entire earth.