GIST 3300 / 5300 Geographic Coordinate System or Grid GIST 3300 / 5300 Last Time Data Classification Methods Take home point: a map is a communication medium and you as the cartographer or GIS analyst can manipulate the appearance of a map to reinforce a point of view using different classification methods 1
Geographic Coordinate System or Grid - Geographic Coordinate System - Cartesian vs spherical coordinate system - properties of latitude (parallels) - properties of longitude (meridians) - longitude and time - describing coordinates - latitude and longitude in a GIS - distinguishing hemispheres in a GIS Geographic Coordinate System or Grid GIS represents reality, but it is not reality - To be useful GIS maps need to accurately represent locations of things or features in the real world on a map - To do this we need a standard framework to help us define locations 2
Geographic Coordinate System or Grid - We call these frameworks reference systems - Reference systems are a set of lines of known location that can be used to determine the locations of features - In a GIS we call these reference systems: coordinate systems By understanding coordinate systems, you will be able to manage your data in a way that increases the accuracy of your GIS maps and all the work you do with them. Geographic Coordinate System or Grid - if the earth was flat - we could use a Cartesian coordinate system Cartesian coordinates describe locations on a flat or planar surface Rene Descartes (0,0) Cartesian coordinate system - specifies each point uniquely in a plane by a pair of numerical coordinates - which are the signed distances to the point from two fixed perpendicular directed lines - measured in the same unit of length (0,0) 3
Geographic Coordinate System or Grid - But the earth is not flat so Cartesian coordinates do not work - So we need a different type of reference system to locate places on the spherical earth - The network of intersecting lines (longitude and latitude lines) form the geographic coordinate system or geographic grid Geographic Coordinate System or Grid Geographic Coordinate System = synonymous with Geographic Grid Geographic Grid a reference system or location framework to locate features on earth A term for the set of intersecting latitude and longitude lines is a graticule 4
Geographic Coordinate System or Grid - based upon angular measurements (not planar) - measurements expressed in degrees, minutes and seconds - A degree is 1/360 of a circle - each degree can be divided into 60 minutes - each minute can be divided into 60 seconds To describe the location of Peoria, Illinois we would say it is at 40 degrees N. Latitude and 90 degrees W. Longitude Geographic Grid Spherical coordinate system - these degrees are measured as angles from the center of the earth to a point on the surface. That is why we call latitude/longitude angular coordinates So from the Center of Earth at the equator, if we go up 30 degrees north we would be at New Orleans. 5
Geographic Grid Latitude (parallels) Definition: east-west lines used to measure the arc distance north and south of the Equator Geographic Grid Latitude (also called parallels) - properties - are parallel to one another - encircle the globe - can range from 0 to 90 degrees N & S 6
Geographic Grid Important Lines of Latitude North Pole 90 o Arctic Circle 66.5 o N Tropic of Cancer 23.5 o N Equator 0 o Tropic of Capricorn 23.5 o S Antarctic Circle 66.5 o S South Pole 90 o Geographic Grid Longitude (also called meridians) Definition: north-south lines used to measure the arc distance east and west of the Prime Meridian 7
Geographic Grid Longitude (meridians) - properties - converge at the poles - do not encircle the globe - range from 0 to 180 degrees E & W Geographic Grid Two important lines of longitude - the Prime Meridian - 0 o of longitude - runs through the Royal Observatory in Greenwich, England - International Dateline - 180 o of longitude - runs through the Pacific Ocean opposite Greenwich Western Hemisphere Eastern Hemisphere 8
Geographic Grid The Prime Meridian (today) is only one of many historic PMs Washington, D.C. (77 3 2.3 W; Washington Meridian) Philadelphia (75 10 12 W) Canary Islands (18 03' W) Lisbon, Portugal (9 07 54.862 W) Madrid, Spain (3 41 16.58 W) Prime Meridian (0 o ) Greenwich, England Paris, France (2 20 14.025 E; Paris Meridian) Brussels, Belgium (4 22 4.71 E) Berne, Switzerland (7 26 22.5 E) Pisa, Italy (10 24 E) Oslo (Kristiania), Norway (10 43 22.5 E) Rome, Italy Meridian of Mount Mario (12 27 08.4 E;) Copenhagen, Denmark (12 34 32.25 E) Stockholm (at the observatory), Sweden (18 3 29.8 E) Warsaw, Poland (21 00 42 E; Warsaw Meridian) Oradea, Romania (21 55 16 E) Alexandria, Egypt (29 53' E) Saint Petersburg, Russia Pulkovo Meridian (30 19 42.09 E) Great Pyramid of Giza (31 8 3.69 E, 1884) Jerusalem (35 13 46 E; the large dome of the Church of the Holy Sepulchre) Mecca (39 49 E) Map of Texas 1816 Longitude West from Washington 24 Longitude 23 West 22 from 21 Washington 20 19 Longitude West from Washington 9
260 270 280 290 300. degrees This map starts at some 0 degree meridian and keep going to 360 degrees around the world The point is the notion of a PM location is arbitrary so are hemispheres Geographic Grid The Prime Meridian - what we use today is an arbitrary meridian - runs through the Royal Observatory in Greenwich, England - first established by Sir George Airy in 1851 - by 1884 two-thirds of all ships used it as the reference on their maps - international conference held in Washington, D.C. in 1884 - delegates represented 25 nations prominent sea-faring nations - delegates selected the Greenwich Meridian owing to its wide use - only France abstained - used the Paris Meridian for several more decades 10
Geographic Grid The Prime Meridian - located outside of London Royal Observatory, Greenwich, England Prime Meridian Geographic Grid The Prime Meridian - located outside of London 11
Geographic Grid Longitude and Time - the Earth rotates on its polar axis once each day - the rotation covers 360 o in 24 hours - if we divide 360 o / 24 hours - the rotation covers 15 o / hour Geographic Grid - this is the basis for the 24 world time zones - each time zone covers 15 o of longitude (360 / 24 ) International Dateline 180 o of longitude Greenwich Mean Time 0 o of longitude 12
Geographic Grid Describing Coordinates When describing coordinates, by convention, we usually give the latitude (N or S) first, followed by the longitude (E or W). For greater precision, each degree can be subdivided into 60 minutes and each minute can be subdivided into 60 seconds. A typical geographic coordinate might then be expressed as: 24 15' 30" N, 110 38' 12' W. (note: if convert geographic coordinates to Cartesian coordinates latitude represents y-axis and longitude represent x-axis) Remember - Geographic coordinates describe angular distances Geographic Grid Latitude and Longitude in a GIS In a GIS, degrees of latitude and longitude are expressed as decimal degrees. A computer cannot work with data entered in degrees, minutes and seconds. To convert degree/minute/second coordinates to decimal degrees: 1) divide the seconds by 60 (decimal minutes), 2) add this fraction to the minutes, 3) and then divide this sum by 60. 24 15' 30" 24 15' (30"/ 60 ) = 24 15.5 (decimal minutes) 24 (15.5'/ 60 ) = 24.2583 (decimal degrees) 13
Geographic Grid Distinguishing Hemispheres in a GIS Environment It is also important to note that positive and negative values are assigned to coordinates in a GIS to distinguish between the hemispheres. With respect to LATITUDE, - northern hemisphere coordinates are positive (+) - and southern hemisphere coordinates are negative (-). With respect to LONGITUDE, - eastern hemisphere coordinates are positive (+) - and western hemisphere coordinates are negative (-). + 24.2583, -110.6367 S lat itude longitude Y X lat, lon N 0 o W 0 o E + + + Housekeeping Fun with the Esri e-learning site If you are having difficulty accessing the homework assignments: - Log out of the website - Completely close your browser - Open a new browser - Log in again to refresh your session You should be able to access the e-learning assignments 14
Housekeeping Uploading Lab Assignments to your Student Folder Make sure you upload a PDF or JPG as assigned If you upload a.mxd alone that won t work! The data are not stored in the MXD. The data are stored separately on disk! TAs can open the MXD, but they won t see any of your layers since their path will be different than yours. Remember an.mxd is a document that only references the data on disk (though it s pathname to the data). 15
The Geographic Coordinate System or Grid GEOGRAPHIC INFORMATION SYSTEMS Lecture 06: Geographic Coordinate System or Grid - if the Earth was flat we could use a Cartesian (x,y) coordinate system to locate places on the surface - because the Earth is a spheroid, this approach doesn t work so we must use a spherical coordinate system - the geographic grid is a spherical coordinate system based on latitude and longitude - lines of latitude and longitude are measured using degrees, minutes and seconds (angular measurement) - these angular measurements for latitude and longitude are referenced from the center of the Earth Latitude (also called parallels) - east west line used to measure the arc (angular) distance north and south of the Equator - range from 0 to 90 north and south of the Equator - encircle the globe (except for north and south poles) - lines of latitude are parallel to one another - important lines of latitude include: - North Pole (90 N) and South Pole (90 S) - defined by the Earth s polar axis of rotation - Equator (0 ) - the latitude that bisects the Earth s polar axis of rotation - Tropic of Cancer (23.5 N) and Tropic of Capricorn (23.5 S) - the most northerly and southerly latitude where the sun is directly overhead (90 o ) - on an annual basis, the declination of the sun varies between the two tropics - Arctic Circle (66.5 N) and Antarctic Circle (66.5 S) - the most northerly and southerly latitude where the daylength can be 0 or 24 hours - defined by the Circle of Illumination Longitude (also called meridians) - north-south lines used to measure the arc (angular) distance east and west of the Prime Meridian - range from 0 to 180 east and west of the Prime Meridian - lines of longitude do not encircle the globe (they extend from pole to pole) - meridians converge at the north and south poles - important lines of longitude include: - Prime meridian in Greenwich, England (0 ) - International Dateline - mid Pacific (180 ) - Prime Meridian only of one of many that have been used over the years - runs through the Royal Observatory in Greenwich, England - the Prime Meridian was established by an international convention in 1884 Longitude and Time - the earth rotates 360 in 24 hours or 15 per hour - this is the basis for the world s 24 time zones where (ideally) each time zone covers 15 of longitude Describing Coordinates - by convention, we usually give latitude first, followed by longitude - for greater precision, each degree of latitude or longitude can be subdivided into 60 minutes - for still greater precision, each minute can be divided into 60 seconds example: 24 15' 30" N, 110 38' 12' W. Latitude and Longitude in a GIS - in a GIS, latitude and longitude are expressed as decimal degrees - know how to convert degrees, minutes and seconds to decimal degrees - know how to differentiate the hemispheres as positive or negative (+, -) decimal degrees - e.g. western and southern hemispheres are expressed as negative values same example expressed in decimal degrees: 24.2583, -110.6367 Demonstration 1: Showed a map document of the world with the North Pole in the center. Copyright 2016, Kevin Mulligan, Lucia Barbato, Texas Tech University
The Prime Meridian was shown running through Greenwich England so the 0 meridian runs from the center of the map (North Pole) to the bottom of the map (South Pole). On the top of the map is a line running from the North Pole to the top of the map labeled 180. This meridian is the International Date Line. The IDL is an arbitrary or imaginary line on the surface of the Earth that runs from the North Pole to the South Pole and demarcates the change of one calendar day to the next. For the most part the IDL runs through the middle of the Pacific Ocean roughly following the 180 degree line of longitude but deviates to pass around some territories and island groups. If you cross the IDL westbound you add 24 hours to your clock advancing the calendar date by one date. If you are traveling eastbound and cross the IDL you must subtract 24 hours and move the date back one. Notice: with the PM at the bottom of the screen the eastern hemisphere is on right and the western hemisphere is on the left as you would customarily see on most maps. (E to W) Demo: Customize > Toolbars > Data Frame Tools >. Rotate the Earth 180 degrees so that the PM is at the top. When the PM at the top of the map notice that the hemispheres are switched, so that the eastern hemisphere is on the left. Kind of cool! If time: Demonstration 2: MapScale map document to show how scale works on a world map. Representative Fraction or Absolute Scale The map was set up on a 40 x 30 piece of paper in the Layout View where we can add map elements to create our map. In Lecture 3 we talked about bar scales, verbal scales and representative fraction. In lab you might have already seen a bar scale. In ArcMap we can insert different types of scales. Insert > Scale Text > Absolute Scale > OK (means the same as a representative fraction or RF). The absolute scale should display at the same as shown the scale display area in ArcMap. If the scale display is changed to 1:100M. The RF changes as well. The problem is what if you want to measure a distance in Kilometers? Not so easy. Have to do a little math to convert say inches to km. Scale Bars Copyright 2016, Kevin Mulligan, Lucia Barbato, Texas Tech University
There are many different scale bar formats available: Insert menu> Scale Bar > Scroll through the options. Add another scale bar: Alternating Scale Bar 2 > Properties > Adjust width > division value 5000 > number of divisions 4 > Subdivisions 0> Units KM. Numbers and Marks > frequency > divisions. Format tab > Change font to Arial 48 and size to 18 point. Demo 2 Data has a scale associated with it Displayed another map document with Texas counties. The first map has a scale of I: ~9M. It is also important to consider that data we see are also created at a specific scale. So keep in mind that the map has a scale and also the data has a scale associated with it. The TXCnty_Esri data are very generalized. Zoomed to Galveston Coast. Coast lines appears straight and jagged not very detailed. These data were created at a scale of 1:1M and not intended for use at scales much larger than that. TxCounties_USGS layer is slightly more detailed at the same map scale. The data were digitized at a scale of about 1:50,000. StratMap layer. StratMap or Strategic Map of Texas data are extremely detailed data at the same map scale. The data were digitized at a scale of 1:24,000. So when you are searching for data it is important to work with data that was developed at a scale that is appropriate to the type of mapping work you are doing. Copyright 2016, Kevin Mulligan, Lucia Barbato, Texas Tech University