Presentation on theme: "Maps and GIS Created by Lisa Bingham University of Stavanger, Norway."— Presentation transcript:
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
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
Title Scale bar Grid coordinates Legend Some maps have north arrows or compass roses, or may include projection information. This map does not. Compiler and publication information Inset map Where is the title? Where is the legend? Where is the inset map? Where is the scale bar? Where is the scale? Where are the grid coordinates? Where is the north arrow? Where is the publication information? Where are the graphs? Graphs
Familiarize yourself with the map.
What does the map tell you? Mica-rich in the south Gold in north-central Diamonds with gold in the northeast Diamond production decreasing Mineral-rich in the north Mineral-poor in the center Minerals in the south If you represented a mining company, where would you look for: gold? diamonds? bauxite? radioactive minerals?
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?
What can be said about the elevation in this area (northeast corner of the previous map)?
Steep slopes V shape Less steep area Coastline
What can be said about the elevation in this area (central area of the large map)?
Coastline Flat area Steeper area with very curvy contours High point or depression? Flat area
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 spaced from 0 o at equator to 90 o at poles. 60 nautical miles (~ 110 km)/1 o, ~1.8 km/minute and ~ 30 m/second of latitude. N. latitudes are positive, S. latitudes are negative. From M. Helper, University of Texas, 2008 Equator
Longitude facts: Lines of longitude (meridians) converge at the poles; the distance of a degree of longitude varies with latitude. Zero longitude is the Prime (Greenwich) Meridian (PM); longitude is measured from o east and west of the PM. East longitudes are positive, West longitudes are negative. P.M. 180 o From M. Helper, University of Texas, 2008
Units of Measure Decimal degrees (DD), e.g o, o – order by longitude, then latitude – Format used by ArcGIS software Degrees, Minutes, Seconds (DMS), e.g. – 90 o 30’ 00”, 35 o 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. Map distance Globe distance Globe distance Earth distance Scale 1: 42,000,000 Scale Factor (for specific points) Mercator Projection EarthGlobe Map From M. Helper, University of Texas, 2008
Inflatable globe demonstration Blown up and Cut up
Laying the earth flat Systematic rendering of Latitude ( ) & Longitude ( ) to rectangular (x, y) coordinates: Geographic Coordinates ( ) Projected Coordinates (x, y) 0, 0 x y Map Projection From M. Helper, University of Texas, 2008
Laying the earth flat “Geographic” display – no projection – x = , y = – Grid lines have same scale and spacing y x From M. Helper, University of Texas, 2008
“Geographic” Display Distance and areas distorted by varying amounts (scale not true); e.g. high latitudes y x From M. Helper, University of Texas, 2008
Projected Display E.g. Mercator projection: – x = – y = ln [tan + sec ] y From M. Helper, University of Texas, 2008
Laying the earth flat How? Projection types: a A’ b B’ a A’ b B’ a A’ b B’ OrthographicGnomonicStereographic T T’ T T 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: 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 GeologyDEM Digital elevation model HydrographyRoads From M. Helper, University of Texas, 2008
Features have locations Origin (0, 0) X axis Y axis Stavanger X = m Y = m 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 : First hand-held, “mapping-grade” receivers : 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? z Clock errors will cause spheres of position (solid lines) to miss intersecting at a point. Adjust receiver clock slightly forward will cause larger T(=larger sphere; dashed) and intersection at point. z Requires 4 SVs, not 3 as shown, for clock error & X, Y, Z From M. Helper, University of Texas, 2008
Satellite Positioning Geocenter Known Orbit Observe T Determine 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 (4 th 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
200 km 50 km Sources of Error SV clock error (~1.5 m) Ionospheric Refraction (~ 5 m) (Can correct with L1 & L2 Ts) Tropospheric Delay (~ 0.5 m) Multipathing (~0.5 m) + GDOP (errors x 4-6) (Geometric dilution of precision) L2 L1 Satellite Orbit Errors (~2.5 m) From M. Helper, University of Texas, 2008
Satellite Constellation Must have a good spread of satellites 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.
An x, y coordinate system references the real- world location. Shapefiles and feature classes (file types) are vector data. Appropriate for discrete data where boundaries are needed. – Pipeline location.
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 Oman
Using Satellite Data with GIS – Digitize buildings and roads – Digitize faults, scarps, rivers, or elevation Beijing, China Oman
ArcMap document Map area Table of contents Title bar 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 GIS Data Depot data.geocomm.com DIVA-GIS Norwegian Geological Survey (NGU) United States Geological Survey Many others
General Websites: X,Y Data (Need Converting) USGS NEIC Earthquake Database
General Websites: Grids (May Need Converting) General Bathymetric Chart of the Oceans (GEBCO) CGIAR-CSI SRTM Processed NASA satellite topography data Scripps Institution of Oceanography NGDC World Magnetic Anomaly Map
General Websites: Maps (Need georeferencing) The University of Texas at Austin Perry- Casta ñ eda Library Map Collection 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
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 Distortion Differential Scaling Skew TranslationRotation From M. Helper, University of Texas, 2008
General problem is then: Source (x, y)Destination (X’, Y’) (0,0) (1,0) (0,1) ( , ) (501000, ) Control Points “Displacement Link” (1,1) (“Warp”) 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 over- generalized. 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)