Study Guide for Quiz 1 (Lec 1-6) PDF

Study Guides for Quiz 1 (Lectures 1-6) NOTE: Some knowledge points require the previous pages as important contexts to understand them. Please do NOT only read the marked pages. Lecture 1: What is spatial data model? (p35) Objects in a spatial database plus the relationships among...

Study Guides for Quiz 1 (Lectures 1-6) NOTE: Some knowledge points require the previous pages as important contexts to understand them. Please do NOT only read the marked pages. Lecture 1: What is spatial data model? (p35) Objects in a spatial database plus the relationships among them Formal means of representing and manipulating spatially referenced info What are vector and raster data models? Examples of vector and raster models (p37-38)? Vector: comprised of vertices and paths (a real-world feature is presented in a map by sets of points, lines, and polygons) Raster: set of grid cells (pixels) with row and column (X, Y) locations, each cell (pixel) has a value What is discrete and continuous data? Examples of discrete and continuous data (p39)? Discrete data: exists in a defined location/space Lookout tower (point). Stream (line). Snail habitat (polygon) Continuous data: exists everywhere Elevation Precipitation What are the three basic shapes of vector data models? What are their important characteristics? What are some examples of them? (p40-41) Points - no area or dimension; position only; (x,y) (CRS) Location of schools and parks, bus stops, traffic lights Lines - length but no area; series of connected points (vertices) Roads, highways, rivers, streams, boundaries, trails  Polygons - both length and area +perimeter; closed area formed by connecting at least 3 points (vertices) Lakes, parks, forest areas, counties, states, countries What are the two common raster types? Examples? (p44) Thematic raster - specific categories or themes (value corresponds to an attribute) SINGLE BAND measure quantity or classification Land cover, soil types, population density Image raster - pixels that capture continuous data from photos or satellite images SEVERAL BANDS represent reflected or emitted light/energy Lecture 2: Important characteristics of vector data model (p6). What is vector data model composed of? (p8) All entities are represented by coordinate pairs in proper order (start to end) Composed of: coordinates (polygons) and attributes (land use + area) - A vector data model is essentially formulted by points stored by ther real earth coordinates - Lines and areas are built from sequences of points that are stored in order - Lines have a direction from the ordering of the points (start to end point) - Polygons can be built from points or lines - Vectors can store info ab topology What are the basic units in vector topography (p10) points - points lines - arcs nodes - start/ending points vertex = intermediate point in a line to define shape areas (polygons) - built from arcs What are the four principles of vector topography? What do they mean? (p13-14) 1. Connectivity (no gap) - lines and points are connected in a spatial network 2. Adjacency (no gap) - relationship between neighboring polygons 3. Containment - where one feature is contained within another (polygon a in polygon b)  4. Planarity - all points, lines, and polygons are on the same plane What are the advantages of vector models? (p16) 1. Can represent point, line, and area features very accurately 2. Far more efficient than grids 3. Work well with digitizing pen and light plotting devices 4. BUT vectores ARE NOT GOOD at displaying continuous data (printing) Important characteristics of raster data models (p18) Regular grid of cells evenly spaced, each cell has an attribute value (ONE value) even if its missing data, has resolution, each cell = evenly spaces in x y direction What are the three most common type of raster data? (p21) Land cover Terrain Satellite images Pros and cons of raster models? (p25-26) 1. Faster, but less accurate 2. Easy to understand and easy to print 3. Points and lines represented by cells containing the same value 4. Lines can become fat 5. Each cell can only have one value (one attribute per cell) Large vs small scale maps (p32-33) Small scale maps = less details (zoomed out) (1:300,000) Large scale maps = more details (zoomed in) (1:1,000) What are some cartographic design decision principles (p44). Examples (p45) Data to plot Scale, size, shape Symbol shape, sizes, and patterns Labeling, font and size Legend properties, size, and borders  Placement of all these elements on the map colorblindess Lecture 3 What are the common map elements? (p6) 1. Title - short and sweet 2. Focal element - fulfills the title 3. Supportive elements Legend Scale bar North arrow 4. Balance Elements evenly weighted No empty spaces or crowded elements What are some basic map types? What are choropleth maps? (p8-9) Cloropleth map: a thematic map with shaded or patterned in proportion to the measurement of the statistical variable What is an isoline? What is a contour map? (p19) Contour map: using lines to represent elevations and the shape of the terrain Isoline = a line connecting points of equal value (like temp, elevation, etc)  How is a color represented in an RGB color model? (p27) Mixtures of red, green, and blue Each primary color brightness is indicated on a scale of 0(black) to 255(bright) White is the full intensity of all these colors What is color contrast, color harmonies, and warm vs cool colors? (p29) Color contrast High - opposites on the color wheel Low - near eachother on the color wheel Color harmonies Complimentary colors (high contrast) Analogous colors (low contrast) Warm vs cool colors Warm - red, orange, yellow Cool - green, blue, purple How to choose color to represent map values? (p30-32) 1. Use different colors for categories 2. Use different shades of same color for quantities 3. Ise shades of two colors for divergent quantities (+ to -)  What are different types of attributes? What are some examples of them? How to map them? (p36-41) Nominal: names or uniquely identifies objects County names, airport names, tax ID numbers Ordinal: ranks categories along an arbitrary scale (unique values / graduated color) Snail habitat: (0) unsuitable, (1) marginal, (2) acceptable, (3) ideal Categorical: separate features into distinct groups or classes (either text or color) Rock type, volcano type, highway class Interval: places values along a regular numeric scale; can be - or + values Temperature (can be negative), time, SAT scores  Ratio: places values along a regular scale with a meaningful 0 point Population of state capitals, age, mass Lecture 4 What are the typical mapping approaches to represent different types of data (p5-8) CHANGE IN ENTITY/CATEGORY Nominal data: single symbol map with optional labels Cateogorical data: use unique color to map into distinct groups or classes Ordinal: use a unique values map or graduated color maps CHANGE IN QUANTITY Inverval & ratio: both must be divided into classes before mapping - Variations in: size of symbols, thickness, and hue What are some characteristics of displaying discrete and continuous raster data? (p11)? THEMATIC RASTER Discrete: Represent objects (roads or land use polygons) Few values Adjacent cells often have same values Values may change abruptly at boundaries  Continuous: (more common) Represent a measurement that occurs everywhere Thousands or millions of values Few adjacent cells have same values Values may change rapidly from cell to cell How to display categorical/ordinal and interval/ratio raster data? (p12) Cateogorical/ordinal - raster uses unique values or discrete color Interval/ratio - (quantities) raster uses classified or stretched display methods What are some principles to symbolize data? (p19) The brain seeks patterns Color is more effective than shape Lecture 5 What are the two common types of coordinate systems? (p2) Spherical & Cartesian What are some characteristics of Cartesian coordinates? (p4) Created by transferring spherical/geographic coordinates to a Cartesian coordinate system Most common for mapping small areas (google maps) Cam introduce small errors due to the conversion What coordinate systems are GCS and PCS based on, respectively (p5) GCS - spherical coordinates (defines where the data is located - longitude and latitude) PCS - planar/cartesian coordinates (how to draw on a flat surface) What are the characteristics of latitude and longitude? (p7)  Latitude - north to south 90 degrees in each hemisphere 0 = equator Longtitude - east to west 180 degrees in each hemisphere 0 = prime meridian How to convert between degree, meter, and second? (p8) Degrees-minutes-seconds (DMS) Decimal degree (DD) 1 degree = 60 min and 1 min = 60 sec 1 degree = 3600 seconds What are some characteristics of GCS? (p10) Since meridians converge at poles, geographic coordinates do NOT form a cartesian coordinate system (use spherical) 1 degree of longitude = 111.3 km at equator 0 1 degree of latitude = 110.6 km at equator. 117.7 km at poles (Earth is not a perfect sphere) Convergence causes distortion in area, distance, angle, and shape when converted into cartesian Lecture 6 What is the geoid? What are some characteristics of geoid? (p7-10) Geoid = a model of global mean sea level that is used to measure precise surface elevations Geoid’s surface defines zero elevation Modeled from gravity differences and is closest to the true shape of earth (too complicated for mapping) Not a physical surface “Reference surface” that fits as closely as possible Cant define locations How to define the spheroid shape of the earth (p17) 1. Semimajor axis (a) and semiminor (b) 2. By (a) and the flattening factor. f=(a-b)/a  What are some principles to model earth as a spheroid (p18-20) Spherioid is chosen to fit one country or a particular area A spherioud that fits one region wont necessarily fit another Example: WGS84 Spherioid that fits one country - local (local datum) Center of spherioid isnt center of earth Global spheroid - fits reasonable well over entire geoid (geocentric - center of spheroid = center of geoid) What is a datum? (p23) A reference for a system of geographic coordinates that serves as a standard measurement (built on top of selected spheroid) Specifies each location on earth’s surface in latitude and longitude What is the difference between a datum and ellipsoid? (p24) Ellipsoid = defines the size and shape of the earth Datum = fixes that ellipsoid to the earth What are horizontal datum and vertical datum? (p26) Horizontal = a collection of specific points (according to longitude and latitude) Vertical = reference surface that is used for measuring heights (altitude) What are local and world-centered datum? (p27) Local = optimizes the shift for the best fit at a particular location World centered = optimizes the fit for the entire earth What are important characteristics of geoid, spheroid, and datum? (p30-32) Geoid (the equipotenetial surface of the earth’s gravity field) Represents the shape that the surface of the oceans (liquid) would  take under the influence of earth’s gravity and rotation alone No mathematical description Spheroid (simplified mathematical model of earth’s surface) Describes 3D shape of earth using a semi major (radius from center to equator) or semi minor axis (radius from center to the pole) or flattening factor Datum (built on top of the selected spheroid and incorporates local variations in elevation) Datum fixes the local lat/long coordinates to the spheroid surface and allows local variations in elevation to be incorporated What are map projections used for? (p34) A systematic rendering of locations from the curved earth surface onto a flat map surface with cartesian coordinate system What are some possible distortions in map projection? (p38) Distortions in shape, area, distance, and direction No flat map can be both equivalent (preserve area) and conformal (preserve angles, shape)