maps and gis

Maps and GIS

Created by Lisa BinghamUniversity of Stavanger, Norway

Course Objectives• Read, understand, and interpret maps• Basic understanding of GIS• Basic understanding of GPS

http://img.moonbuggy.org/the-road-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

Title

ScaleScalebar

Gridcoordinates

Legend Some maps have north arrows or compass roses, or may include projection information. This map does not.

Compiler andpublication 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 goldin the northeast

Diamond production decreasing

Mineral-rich in the northMineral-poor in the centerMinerals 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?

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)?

Steep slopes

V shape

V shape

Less steep area

Coastline

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)?

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 0o at equator to 90o at poles.

60 nautical miles (~ 110 km)/1o, ~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 0-180o east and west of the PM.

East longitudes are positive, West longitudes are negative.

P.M.180o


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”


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.


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 distanceGlobe distance

Globe distanceEarth distance

Scale1: 42,000,000

Scale Factor0.9996

(for specific points)

Mercator ProjectionEarth Globe

Map


Inflatable globe demonstration

Blown upand

Cut up

Laying the earth flat• Systematic rendering of Latitude (f) &

Longitude (l) to rectangular (x, y) coordinates:

Geographic Coordinates(f, l)

Projected Coordinates(x, y)

0, 0 x

y

Map Projection


Laying the earth flat

• “Geographic” display – no projection– x = l, y = f– Grid lines have same scale and spacing

y

x

l

f


“Geographic” Display• Distance and areas distorted by varying amounts

(scale not true); e.g. high latitudes

y

x l

f


Projected Display

• E.g. Mercator projection:– x = l– y = ln [tan f + sec f]

yf

0

90

0 5+


Laying the earth flat• How?Projection types:

a A’

bB’

aA’

bB’

aA’

bB’

Orthographic

Gnomonic

Stereographic

TT’

T T’ TT’


Inflatable globe demonstration

Light shines through

Projection produces distortion of:

• Distance• Area• Angle• ShapeDistortions 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


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)


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


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


A GIS is Composed of Layers

Geology

DEMDigital

elevation model

Hydrography

Roads


Features have locations

Origin (0, 0)

X axis

Y axis

StavangerX = 638539 mY = 8135093 m


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


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


GPS Facts of Note• USA Department of Defense navigation system

– First launch on 22 Feb 1978 – Originally 24 satellites

• Today ~30 satellites for GPS


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)


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.


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


Satellite Positioning

Geocenter

Known

OrbitObserve DT

Determine


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


200 km

50 km

Sources of Error

SV clock error (~1.5 m)

Ionospheric Refraction (~ 5 m)(Can correct with L1 & L2 DTs)

Tropospheric Delay (~ 0.5 m)

Multipathing (~0.5 m)

+ GDOP (errors x 4-6)(Geometric dilution of precision)

L2L1

Satellite Orbit Errors (~2.5 m)


Satellite Constellation

• Must have a good spread of satellites• http://en.wikipedia.org/wiki/

File:ConstellationGPS.gif

GPS Resolution and Map Scales


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 real-world 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, Chinahttp://www.globalsecurity.org

Omanhttp://www.satimagingcorp.com

Using Satellite Data with GIS– Digitize buildings and roads– Digitize faults, scarps, rivers, or

elevation

Beijing, Chinahttp://www.globalsecurity.org

Omanhttp://www.satimagingcorp.com

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

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 Databasehttp://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 SRTMProcessed NASA satellite topography datahttp://srtm.csi.cgiar.org/

• Scripps Institution of Oceanographyhttp://topex.ucsd.edu/marine_topo/

• NGDC World Magnetic Anomaly Mapwww.geomag.us/models/wdmam.html

General Websites: Maps (Need georeferencing)

• The University of Texas at Austin Perry-Castañeda Library Map Collectionwww.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

DistortionDifferential Scaling Skew

TranslationRotation


General problem is then:

Source (x, y)

Destination (X’, Y’)

(0,0) (1,0)

(0,1)

(498100, 3715000)

(501000, 3725000)

Control Points“Displacement Link”

(1,1)

(“Warp”)


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)

Practice: Good or Bad?

maps and gis

Documents

map scalessmallscale

good map

map scalesrepresentations

map centimeter

previous map

graphic scale barmap

mapa concise map titlean

scale baran easy