Maps and GIS Created by Lisa Bingham University of Stavanger, Norway Course Objectives • Read, understand, and interpret maps • Basic understanding of GIS • Basic understanding of GPS http://img.moonbuggy.org/theroad-to-success/ Reading a map Reading maps • Maps relate information – It is up to the viewer to interpret the information – How? • Investigate the map – Identify the parts of the map – Familiarize yourself with the map – Are there graphs? Inset maps? Additional figures? – What is the purpose of the map? What does the map tell you? What information does it relate? What makes a “good” map? • Defined purpose and audience. – These influence what makes a “good” map for the intended audience. – tourist vs. geologist • Avoid cluttering or over-complications • Legible labeling • Coloring and patterns should follow cartographic conventions. Features of a map • • • • A concise map title An easy to read scale bar An easy to read legend, if necessary North arrow if the coordinate system is not clear or if the map is turned to an angle • Legible coordinates at the border of the map • Projection information Identify the parts of a map Locate: •Title •Scale •Scale bar •Legend •Coordinate system or grid markings •Location or inset map •Publication information Where is the title? Title Where is the legend? Where is the inset map? Where is the scale bar? Scale Scale bar Where is the scale? Where are the grid coordinates? Where is the north arrow? Where is the publication information? Compiler and publication information Where are the graphs? Legend Inset map Graphs Some maps have north arrows or compass roses, or may include projection information. This map does not. Grid coordinates Familiarize yourself with the map. What does the map tell you? Mineral-rich in the north Mineral-poor in the center Minerals in the south Diamonds with gold in the northeast Gold in north-central If you represented a mining company, where would you look for: •gold? •diamonds? •bauxite? •radioactive minerals? Mica-rich in the south Diamond production decreasing Understanding Map Scales • Representations: – verbal (1 map centimeter represents 30,000 ground centimeters) – fraction (1:25,000) – graphic (scale bar) • Map scale indicates how much a given distance was reduced to be represented on the map. Understanding Map Scales • Small-scale map depicts large areas, so low resolution. • 1:10,000,000 Understanding Map Scales • Large-scale map depicts small areas, so high resolution. • 1:50,000 • 1,267 inches to 1 mile Small-scale vs. Large-scale Maps • When the scale is written as a fraction, is the fraction very small or very large? – 1/1,000 – 1/100,000 – 1/1,000,000 – 1/5,000,000 – 1/10,000,000 • Identifying a map as small- or large-scale is an exercise of relativity Reading Map Contours • First familiarize yourself with the map • Locate the contour interval • Investigate the contours – Are they close together? Far apart? – Are the very straight? – Are there many concentric circles? – Do the contours shape like V’s or U’s? Elevation Contour What can be said about the elevation in this area (northeast corner of the previous map)? What can be said about the elevation in this area (northeast corner of the previous map)? V shape Steep slopes Coastline V shape Less steep area What can be said about the elevation in this area (central area of the large map)? What can be said about the elevation in this area (central area of the large map)? Flat area Coastline Flat area High point or depression? Steeper area with very curvy contours High point or depression? High point Understanding Coordinate Systems What is a coordinate system? • • A mathematical system used to explain the location of a point on the earth (or other planet). A geographic coordinate system is used to assign geographic locations to objects. – • A global coordinate system of latitude-longitude is one such framework. Another is a planar or Cartesian coordinate system derived from the global framework. Latitude facts: Lines of latitude (parallels) are evenly o o spaced from 0 at equator to 90 at poles. o 60 nautical miles (~ 110 km)/1 , ~1.8 km/minute and ~ 30 m/second of latitude. N. latitudes are positive, S. latitudes are negative. Equator From M. Helper, University of Texas, 2008 Longitude facts: Lines of longitude (meridians) converge at the poles; the distance of a degree of longitude varies with latitude. 180o Zero longitude is the Prime (Greenwich) Meridian (PM); longitude o is measured from 0-180 east and west of the PM. East longitudes are positive, West longitudes are negative. P.M. From M. Helper, University of Texas, 2008 Units of Measure • Decimal degrees (DD), e.g. - 90.50o, 35.40o – order by longitude, then latitude – Format used by ArcGIS software • Degrees, Minutes, Seconds (DMS), e.g. – 90o 30’ 00”, 35o 24’ 00” From M. Helper, University of Texas, 2008 What is a map projection? A map projection is used to portray all or part of the round Earth on a flat surface. This cannot be done without some distortion. Every projection has its own set of advantages and disadvantages. There is no "best" projection. The mapmaker must select the one best suited to the needs, reducing distortion of the most important features. Laying the earth flat • Why? – Need convenient means of measuring and comparing distances, directions, areas, shapes. – Traditional surveying instruments measure in meters or feet, not degrees of longitude and latitude. – Globes are bulky and can’t show detail. • 1:24,000 globe would have diameter of ~ 13 m • Typical globe has scale of ~ 1:42,000,000 – Distance & area computations more complex on a sphere. From M. Helper, University of Texas, 2008 Laying the earth flat • How? – Using projections – transformation of curved earth to a flat map; systematic rendering of the longitude and latitude graticule to rectangular coordinate system. Scale 1: 42,000,000 Scale Factor (for specific points) 0.9996 Map Earth Globe Globe distance Earth distance Map distance Globe distance Mercator Projection From M. Helper, University of Texas, 2008 Inflatable globe demonstration Blown up and Cut up Laying the earth flat • Systematic rendering of Latitude (f) & Longitude (l) to rectangular (x, y) coordinates: y 0, 0 Geographic Coordinates (f, l) x Projected Coordinates (x, y) Map Projection From M. Helper, University of Texas, 2008 Laying the earth flat • “Geographic” display – no projection – x = l, y = f – Grid lines have same scale and spacing y f x l From M. Helper, University of Texas, 2008 “Geographic” Display • Distance and areas distorted by varying amounts (scale not true); e.g. high latitudes f y l x From M. Helper, University of Texas, 2008 Projected Display • E.g. Mercator projection: – x=l – y = ln [tan f + sec f] 90 f 00 y 5+ From M. Helper, University of Texas, 2008 Laying the earth flat • How? Projection types: Orthographic a Gnomonic A’ T T’ B’ b a T b Stereographic A’ T’ B’ A’ a T b T’ B’ From M. Helper, University of Texas, 2008 Inflatable globe demonstration Light shines through Projection produces distortion of: • • • • Distance Area Angle Shape Distortions vary with scale; minute for large-scale maps (e.g. 1:24,000), gross for small-scale maps (e.g. 1: 5,000,000) Goal: find a projection that minimizes distortion of property of interest From M. Helper, University of Texas, 2008 How do I select a projection? • Scale is critical – projection type makes very little difference at large scales • For large regions or continents consider: – Latitude of area • Low latitudes – normal cylindrical • Middle latitudes – conical projection • High latitudes – normal azimuthal – Extent • Broad E-W area (e.g. US) – conical • Broad N-S area (e.g. S. America) – transverse cylindrical – Theme • e.g. Equal area vs. conformal (scale same in all directions) From M. Helper, University of Texas, 2008 How to know which map projection to use? • General guide: http://erg.usgs.gov/isb/pubs/MapProjections/ projections.html • Conventions for different areas or fields of study Overall View of GIS Key Questions and Issues • • • • What is GIS? What are the applications of GIS? How is the real world represented in GIS? What analyses can GIS perform? What does GIS stand for? • GIS is an acronym for “Geographic Information System” What is GIS? • Computerized management and analysis of geographic information • Group of tools (and people) for collection, management, storage, analysis, display and distribution of spatial data and information • Computer-based tool for mapping and analyzing things that exist and events that happen • Refer to readings for other definitions From M. Helper, University of Texas, 2008 GIS Software • There are several GIS software programs available for use. – Open source (not necessarily free) • • • • MapServer TerraView Quantum GIS UDig – Proprietary software • • • • • IDRISI GMT Manifold MapPoint ESRI (used in class) GIS Example From M. Helper, University of Texas, 2008 A GIS is Composed of Layers Geology DEM Digital elevation model Hydrography Roads From M. Helper, University of Texas, 2008 Features have locations Stavanger X = 638539 m Y = 8135093 m X axis Y axis Origin (0, 0) From M. Helper, University of Texas, 2008 Spatial relationships can be queried • What crosses what? • Proximity – What is within a certain distance of what? • Containment - What’s inside of what? • Which features share common attributes? • Many others From M. Helper, University of Texas, 2008 Remember • GIS focuses on geographic information • If something has a location or is associated with a location, it can be mapped. Key Questions and Issues • • • • What is GIS? What are the applications of GIS? How is the real world represented in GIS? What analyses can GIS perform? The Global Positioning System From M. Helper, University of Texas, 2008 GPS Facts of Note • USA Department of Defense navigation system – First launch on 22 Feb 1978 – Originally 24 satellites • Today ~30 satellites for GPS From M. Helper, University of Texas, 2008 GPS Milestones • • • • • • • • • 1978: First satellites launched 1983: GPS declassified 1989: First hand-held receiver 1991: S/A activated (large error in location) 1993: GPS constellation fully operational 1995-1996: First hand-held, “mapping-grade” receivers 1996-1998: GPS on a microchip 1997: First $100 hand-held receiver 2000: S/A off (more accuracy) From M. Helper, University of Texas, 2008 GPS Segments • Space – Satellites (SVs). • Control – Ground stations track SV orbits and monitor clocks, then update this info for each SV, to be broadcast to users. • User – GPS receivers convert SV signals into position, velocity and time estimates. From M. Helper, University of Texas, 2008 How are SV and receiver clocks synchronized? Clock errors will cause spheres of position (solid lines) to miss intersecting at a point. Adjust receiver clock slightly forward will cause larger DT(=larger sphere; dashed) and intersection at point. Requires 4 SVs, not 3 as shown, for clock error & X, Y, Z From M. Helper, University of Texas, 2008 Satellite Positioning Observe DT Determine Orbit Known Geocenter From M. Helper, University of Texas, 2008 3-D (X, Y, Z) One-way Ranging • Intersection of 2 spheres of position yields circle • Intersection of 3 spheres of position yields 2 points of location – One point is position, other is either in space or within earth’s interior – With earth ellipsoid (4th sphere) • Get receiver clock synchronized and X & Y but no Z • Intersection of 4 spheres of position yields XYZ and clock synchronization From M. Helper, University of Texas, 2008 Sources of Error Satellite Orbit Errors (~2.5 m) SV clock error (~1.5 m) L2 L1 Ionospheric Refraction (~ 5 m) (Can correct with L1 & L2 DTs) 50 km Tropospheric Delay (~ 0.5 m) 200 km Multipathing (~0.5 m) + GDOP (errors x 4-6) (Geometric dilution of precision) From M. Helper, University of Texas, 2008 Satellite Constellation • Must have a good spread of satellites • http://en.wikipedia.org/wiki/File:Constellation GPS.gif GPS Resolution and Map Scales From M. Helper, University of Texas, 2008 Familiarization with GIS Software used is ESRI ArcGIS, but concepts are the same with any GIS software program. Vector data Vector data • An x, y coordinate system references the realworld location. • Shapefiles and feature classes (file types) are vector data. • Appropriate for discrete data where boundaries are needed. – Pipeline location. Raster data Raster data • Assign a value to a cell. Raster data • Raster data may be a georeferenced jpg or tiff, or a converted ASCII grid. • Appropriate for continuous data where discrete boundaries are not necessary. – Topography • Grid files – Cells contain Z data. – The smaller a cell size, the higher the resolution. Practical uses of raster data • Simple display of a raster – Topography (elevation) – Bathymetry (depth) – Gravity – Magnetic anomalies Advanced uses of raster data • Additional processing of raster – Changes in morphology – Sediment thickness – Hill shades (Creating texture) – Contours – Topographic profiles – Spatial analysis – Map algebra Using Satellite Data with GIS • GPS Data – Datapoints – Tracks • Remote Sensing Data – Satellite images – RADAR Beijing, China http://www.globalsecurity.org Oman http://www.satimagingcorp.com Using Satellite Data with GIS – Digitize buildings and roads – Digitize faults, scarps, rivers, or elevation Beijing, China http://www.globalsecurity.org Oman http://www.satimagingcorp.com Title bar ArcMap document Map area Table of contents Coordinates Acquiring External Data • Government and non-government agencies may provide free GIS data • Quality – Map purpose influences acceptable quality General Websites: Shapefiles • Norwegian Petroleum Directorate www.npd.no • GIS Data Depot data.geocomm.com • DIVA-GIS www.diva-gis.org/gdata • Norwegian Geological Survey (NGU) www.ngu.no • United States Geological Survey www.usgs.gov • Many others General Websites: X,Y Data (Need Converting) • USGS NEIC Earthquake Database http://neic.usgs.gov/neis/epic/epic.html General Websites: Grids (May Need Converting) • General Bathymetric Chart of the Oceans (GEBCO) www.gebco.net • CGIAR-CSI SRTM Processed NASA satellite topography data http://srtm.csi.cgiar.org/ • Scripps Institution of Oceanography http://topex.ucsd.edu/marine_topo/ • NGDC World Magnetic Anomaly Map www.geomag.us/models/wdmam.html General Websites: Maps (Need georeferencing) • The University of Texas at Austin PerryCastañeda Library Map Collection www.lib.utexas.edu/maps/ • Google Image search Identify features • Select the identify tool. • Click on a feature. Why select features? • • • • Create subsets Find data Find counts of data with certain attributes Find data near a location Select by attributes • Use Select by Attributes wizard • Use when attribute values are known and assigned • Can be unique Select by location • Use select by Location wizard • Location with buffers – What is a buffer? • Location with respect to another dataset Creating and editing shapefiles • Not all data that is needed for a mapping project will be available in GIS format • Some data is extremely expensive to buy • Some data is not available for purchase • Sometimes the GIS technician needs to create new data based on other map layers Georeferencing What is Georeferencing? • It is a process by which locational information (geo) is added (reference) to an image (raster) in a GIS program. • A point on the image is assigned a coordinate pair in two ways: – By lining up the image to a feature – By adding coordinates directly For Example: • Align raster image to vector data (shapefile or feature) Nature of the problem: • Data source registration may differ by: – Rotation – Translation – Distortion Rotation Differential Scaling Translation Skew Distortion From M. Helper, University of Texas, 2008 General problem is then: Control Points (0,1) (1,1) (501000, 3725000) (0,0) (1,0) Source (x, y) (“Warp”) (498100, 3715000) Destination (X’, Y’) From M. Helper, University of Texas, 2008 What images to use? • Trusted sources (published maps from map agencies) • Clear coordinate system markings (Decimal degrees for Geographic Coordinate Systems; Meters for UTM and Mercator, but need a reasonable guess of UTM zone or Mercator) • Clear country boundaries, city locations, major roads, major rivers What images to discard? • Sketchy sources (personal websites or unpublished sources) • Blurry, coarse or very thick country boundaries. These are usually overgeneralized. • Maps that rely on other maps to show their locations (over-use of inset maps) • Exceptions: Very old maps which are not available in an updated form! Digitizing from Georeferenced Image • Obtain information that has not been published in GIS • Obscure publication or out-of-print publication • Error margin depends on overall scale of data (global vs continental vs regional vs country/state vs town) Practice: Good or Bad? Practice: Good or Bad?