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GGR 272 Final Exam Notes

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Don Boyes

Components of a GIS Discrete objects - Locations, attributes A point, lines to represent a river and polygon to represent a - Where is it and the data that you attach to a park; When you add a raster over it, you can no longer access location that distinct feature - Relationships Types of Geodatabase What is a model? - File geodatabase - Simplified version of reality - Newest file format (.gdb) What is a data model? - Microsoft access file format (.mdb ) - Way of organizing and representing data that are Feature Class simplified versions of reality One data type - You start basic and collect longitude and latitude - When we’ve been talking in general terms like a Data models map layer, the more technical term is feature class - Discrete objects, Vector data modek - Cant mix points, lines, polygons in same file - Raster One theme Vector data Model - Have rivers in one feature class and roads in another - Point, it has a coordinate, small point on the surface - Think of them as variables in an equation list, be of the either able to measure distances in a variable - Line, Two joining points - Polygon: Connect 3 or more to create Controls on map design EXAM QUESTION - Geometry Purpose - Attributes (the table associated to the map) - What map will be used for - Records: Rows in a table - Determines: What will be included; General - Fields: columns reference vs. Thematic map some features may be represented with a line or an actual - How will it look? Tourist maps vs. Scientific results area. It is important to think about the scale - Reference map. Depending on who is looking at Raster Data Model map the information can be more accessible to - Continuous surface, certain audiences - As you zoom in closer and closer you get a small - Thematic maps, Show one subject or one theme of square called a cell, the map. Will show elevation and nothing else - Trying to represent continuously when really Reality breaking down into smaller squares - Spatial characteristics of area will affect how it is - In every grid cell you have to decide that number mapped; Chile is long and narrow, the Hawaiian - Coordinate system used in raster grid, rows and islands are small and spread out columns - You can change the shape of a country Raster Data Model: Cell values Available data - Each cell has one value, Integer or real - Amount and quality of data available will affect your - When a data set is created you have to decide if its map. Missing data? Poor measurements? real or an integer Scale - The level of precision you get can only be round - If you’re making a map of Canada you are creating numbers rather than arbitrary ones at a certain scale to show the country, the detail will - Attribute table: Always have at least 2 columns be much less compared to a smaller one, Must have o Value correct data for the data scale o Count Audience The size of the squares are called Spatial resolution (30m) - Maps should be easy to understand for the intended - This data set has a spatial resolution of 30m audience, Is your audience familiar with the area?, - The smaller the cell the higher resolution know their level of training - It depends on what you are using it for Conditions of use Resolution and Values - Under what conditions will the map be used, On - One value per cell screen, on paper, viewing distance - Implied no variability within a cell Technical limits Mapping a pond; Insert a raster on top of it, depending on the - Printer; Quality, Size of output. Colour vs. Black and scale it will either lose something, When you decrease a scale white by half you quadruple the data - Digital display, Size: smartphone, tablet, laptop, Vector Vs. Raster desk Discrete  vector data model - Internet Continuous  raster data model - Connection speed (e.g. 3G, LTE, Dial-up, wifi, DSL) Design Principles Latitude (Parallels) Speech and text vs. Graphics - Earth rotates around an axis - Origin is where the equator and north and south - Eyes dart over image and process that information axis meet all at once Visual hierarchy Longitude - Things that are more important versus things that Start at the north pole are less important, this map does not have strong Degrees east anmd west of the prim meridian and international date line visual hierarchy - Visually indicate relative importance Prime meridian runs through Greenwich England - Visually communicate - Chosen in 1884 o Similarities - Was already basis for US time zones, most sea o Differences charts - 72% of the worlds commerce depended on o Relationships - Changes in visual level indicate hierarchy Greenwich being the prime meridian - The thing in the foreground is known as the figure Graticule Lines of longitude and latitude intersecting and the background is known as the ground Measuring distance: Angles are not good at measuring, if you Contrast measure from one grid line to another in a distance of 30 degrees, everywhere along the longitude is 30 degrees - Contrast between objects and background - Use sparingly Lat/Long coordinates - Just changing thickness of the lines - Sexagesimal (base 60) system - Legibility, putting a halo around it and bolding the - Degrees, minutes, seconds (DMS) o 142 32', 32 font - + longitude past Prime, -long before Legibility - Lines, patterns, shapes and colours should be Degrees, Minutes, Seconds  decimal Degrees distinct from one another - 120 8' 6'' - Size, Symbols large enough to be identified. - D + (m/60) + (s/3600) - 121 + (8/60) + (6/36000) Consider viewing distance. Large poster vs. Page- - 121.135 size map Map Elements Decimal Degrees  Degrees, minutes Map Scale - 121.135 - .135 x 60 = 8.1 - Need map scale to calculate distance - .1 x (3600) = 32 - Map distance/ground distance - Always expressed as 1/something The Earth is not round (Ellipsoid) - If we go to a map and see the distance is 10cm and Over time, different people have made different the scale is 1:5000 measurements of the amount of flattening Flattening o 1cm on map o Scale 1:5000 F= 1/300 o 1/5000 = 10cm/x Distinguish the different ellipsoids o X=10/5000 If the Earth was a sphere o = 50000cm or 50 m And we drew our angles Geocentric Latitude Expressing map scale; Representative fraction 1/25000, Statement scale: "one inch to one mile, Bar scale If you measure an angle at 45 degrees it goes through the Is it a large or small scale map? centre of the earth called geocentric latitude. If you are Typography treating the earth as a sphere Geodetic Latitude Legibility: Masks, Halo, Callout, Avoid over printing using If you treat the Earth as an ellipsoid, the line of 45 degrees A halo over words, Alignment and Centre extended to the surface of the Earth does not go through the The Earth and its Coordinate system centre Distance measurements Earth as sphere If you treat the Earth as a sphere to measure the distance you Angular unit of measure (measured in degrees) Talking about an angle horizontally and vertically will be off by 1km for every 110 (1¬%)1:5 million or smaller: not noticeable, use geocentric 1:1 million or larger: noticeable, use geodetic Ellipsoid Used t approximate the shape of the Earth for different parts of the world How do we specify where the ellipsoid that we're using is located Datum If Sphere changes to Ellipsoid Links Ellipsoid (model) to the Earth (real) Based on millions of measurements made by ground surveying of satellite Specifies: Ellipsoid used and its location Point on ellipsoid linked to point on Earth (the origin, from which all other points are calculated Datum Comparison datum specifies an ellipsoid and where its connect Earth-Centered datum specifies the earth Local Datum specifies the specific location it is used Datum's. Hundreds of different ellipsoids and datums NAD 27 vs. NAD 83 Datum Elements NAD27 NAD83 Ellipsoid Clarke 1866 GRS 80 Semi-Major Axis 6378206.4m 6378137.0 Datum Origin Meades Ranch Centre of Earth Kansas Mass Control Point 250000 Best Fitting North America World Wide Use NAD83 anywhere in world NAD27 local datum Vertical Position Geographic coordinate system The sea is the most common reference point Like if they wanted to measure the elevation of the peak of a Consists of: Angular unit of measure mountain, they would extrapolate the sea elevation Prime meridian underneath the mountain and measure from there Datum: Specifies an ellipsoid Changing Datum Geographic coordinate system - Angular unit of measure - Prime meridian - Datum o Based on an ellipsoid o If you change the datum, you are changing the geographic coordinate system, so your Geoid height is the difference between the ellipsoid and the coordinates will change geoid Determining latitude on an ellipsoid Geoid: Most accurate way to determine vertical position - If you use an angle of 45 degrees on a sphere of a Ellipsoid: Much easier to make maps from than geoids certain feature, when you change to an ellipsoid the (mathematically simpler to calculate positions, distances) coordinates will appear different So accurate measurements are made from the geoid, and Geographic coordinates then adjusted to fit on an ellipsoid. The Datum (and, therefore, the ellipsoid) is the frame of Mean sea level reference for the coordinates Measure water level at same place for 20 years When you map angular coordinates, you must use the same data that was used to originally measure them They average out the high and low tides Mean Sea Level (MSL) will still vary with location, Data Acquisition temperature, air pressure, salinity, etc. Must know datum used to create Data Sea level: Settles at lowest possible point, measure water If wrong one used, will have measurement errors, objects may level at same place, average out high and low If earth was perfectly spherical, sea level would be some everywhere even over land, Gravity: not consistent everywhere on earth, drawn away from areas of lower gravity, collects and bulges above areas of higher gravity, can still measure any elevation relative to sea level Map Projections Characteristics Globe vs. Map Projection Class: Cylindrical, Conic, Planar Globe: 3D, Expensive, cumbersome, no detail, but no distortion Map: 2D, Easier to measure distance, area, direction, Can show more detail, Easy to work with, portable and cheaper Distortion Transferring All Points from 3D to 2D Case:
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