A kind reminder on distractions such as phone use, noise (see
syllabus). Please allow fellow students to focus.
E.G. please always turn off your cell phone or put it on vibrate mode for class
GIS for environmental management
Dr. William James Smith, Jr.
Assistant Professor of Environmental Studies, UNLV
Adjunct Assistant Professor in Geography, The University of Iowa
GRADUATE STUDENTS MUST PUT THEIR FINISHED PRODUCTS
FOR LABS 7, 8, 9
ON THEIR OWN WEB SITE – OPTIONAL FOR UNDERGRADS.
YOU NEED YOUR BOOKS NEXT WEEK! UPDATE ON SOFTWARE
ISSUES
I am able to setup the first opening hour for Spring 2006.
Every Friday from 1:30pm to 5pm.
State of your labs and exercises and databank
Cartographic roots
and map projections
Cartography
The science that deals with the construction, use, and principles behind
maps and map use.
Old fashioned cartographers worked strictly on paper…
but they are not the oldest -ancient Greek Ptolemy (father of latitude and longitude and map projections).
How could we map these stats (provide x, y, z coords?)
Map scale and projections
The shape of the earth
But paper is!
Nevertheless, earth is a oblate ellipsoid or spheroid (not a sphere
since it is a little wide around the equator than tall from pole to pole.
Remote sensing and improving global position technology
has improved ellipsoid estimation, allowing better measurement of
the elevation of every point on earth, including sea level! This is called
the datum.
Newer datums have been calculated using the center of the earth as
the reference point (instead of a point on the ground).
In mapping the US we will often use the datum introduced in 1983
called the North American Datum (NAD 83) -- there is still some error.
This is part of the geodetic reference system (GRS80) used internationally.
The U.S. military adopted much of this work but refined the values to
create the world geodetic system (WGS84).
This matters to you because when you use or compare maps you
need to know the datum and ellipsoid reference information, as at
large scales (more detailed) there can be significant differences,
especially in elevation.
You also need to know this when using a GPS receiver due to
differences in coordinates.
But what if I need extra accuracy?!
The science of geodesy, which measures the earth’s size, shape, and
gravitational fields exactly has resulted in mapping out of local variations
from the ellipsoid and calls the surface it produces a geoid.
Truth is cartographers often use the sphere as the reference base.
For finer detail (large scale) maps and maps that are very much smaller
(e.g. around 1:100,000) this can produce big differences.
What is map scale?
EVERY map has scale -- be it paper or digital, and every map you use
will represent a REDUCED representation of the world… or of what
use would it be (1:1)?!
Representative fraction is the term used for defining the amount of
scaling. This is the ratio of distances on the map to the distances on the
ground.
A model train is usually about 1:40 scale, meaning
every distance on the model is one-fortieth of its size on the real train.
But the world is so big
we have to get some
small values for the
representative fractions!
1: 100,000
According to various measurements the distance around the “average
world” is 40,078,346.23 meters (24,903.22 miles).
Representative fraction map distance (m)
1:400,000,000
.10002
(earth mapped onto a gumball)
1:40,000,000
1.0002
(earth mapped onto a basketball)
1:24,000
1,666.99
distance in feet (approx)
.328 (3.9 inches)
3.28
5,469 (1.036 miles)
* A 1:1,000 map with lots of detail would mean the equator on the map
would be twice the length of Manhattan Island.
http://convert.french-property.co.uk/
* A 1:1,000 map with lots of detail would mean the equator on the map
would be twice the length of Manhattan Island.
http://convert.french-property.co.uk/
Most national GIS mapping for the U.S. is between 1:1,000,000 and
1:24,000.
Understanding the right scale for the level of detail needed is vital.
GIS allows one to zoom in and zoom out, but you still must make
good choices in map making, and if the details come from data you
pulled from a map at, say, 1:100,000 scale, then zooming in on the
same data might make them look bigger, but there is not the data of
a 1:10,000 map!
Demo on NV Quad
But, even with the right scale, we still have to fit a ellipsoid to a flat
screen or piece of paper!
The part of cartography that deals with this is called map projections.
You can’t memorize every potential map projection and where it is
appropriate for in the world, but we can define general groups and
explore examples together.
Distance between Lines If you divide the
circumference of the earth (approximately
25,000 miles) by 360 degrees, the distance
on the earth's surface for each one degree
of latitude or longitude is just over 69
miles, or 111 km.
Minutes and Seconds For precision
purposes, degrees of longitude and latitude
have been divided into minutes (') and
seconds ("). There are 60 minutes in each
degree. Each minute is divided into 60
seconds. Seconds can be further divided
into tenths, hundredths, or even
thousandths.
You are here - http://www.geocode.com/modules.php?name=TestDrive_Eagle
Map projections are attempts to portray the surface of the earth or
a portion of the earth on a flat surface.
Some distortions of conformality, distance, direction, scale, and
area always result from this process. shape
Some projections minimize distortions in some of these properties
at the expense of maximizing errors in others.
Some projection are attempts to only moderately distort all of
these properties.
* Conformality
- When the scale of a map at any point on the map is the same in
any direction, the projection is conformal. Meridians (lines of
longitude) and parallels (lines of latitude) intersect at right
angles. Shape is preserved locally on conformal maps.
* Distance
- A map is equidistant when it portrays distances from the center
of the projection to any other place on the map.
* Scale
- Scale is the relationship between a distance portrayed on a map
and the same distance on the Earth.
* Area
- When a map portrays areas over the entire map so that all
mapped areas have the same proportional relationship to the areas on
the Earth that they represent, the map is an equal-area map.
shape
Different map projections result in different spatial
relationships between regions.
Four major classes of map projections:
1. Cylindrical projections result from projecting a spherical surface onto a cylinder.
2. Conic projections result from projecting a spherical surface onto a cone.
3. Azimuthal projections result from projecting a spherical surface onto a plane.
4. Miscellaneous projections include unprojected ones such as rectangular
latitude and longitude grids and other examples of that do not fall into the
cylindrical, conic, or azimuthal categories.
The line(s) on the map where the cut falls on the projection act like a globe,
that is, that is an area with no distortion -- the nearer the line the less problems.
If the line coincides with a parallel of latitude then it is a standard parallel.
PP 42-44 Clarke
At http://www.colorado.edu/geography/gcraft/notes/mapproj/mapproj_f.html
Review from “Map projections fall into four general classes.”
Map projection options continued
http://www.lib.utexas.edu/maps/cartographic_reference.html
http://www.swopnet.com/waypoints/
Bottom line
-Larger area mapped = more important the errors due to proj are.
-The proj should fit the application (e.g. calculating areas vs dist.)
*Many GIS can convert geographic coordinates to several map
projections (you will do this next), some can go backwards from
from map coordinates in a projection to lat/long.
-Do not unintentionally mix. E.G. in the U.S., until recently
most 1:24,000 topographic map series of the USGS used a polyconic
projection, the Clarke 1866 ellipsoid, and NAD27 datum
but now, you see a continued shift to NAD83 datum and ellipsoid
named GRS80.
This has “moved” features by as much as 300 meters on the ground
or 12.5 milimeters (.49 inch) on 1:24,000 maps.
Datum and coordinate systems overviews
http://www.colorado.edu/geography/gcraft/notes/datum/datum.html
STOP HERE
http://ccs.unlv.edu/scr/support/labs/questions.asp
I have copied the section of creating web site.
How to create a website using your SCR Computer Labs account?
You can host web pages over the World Wide Web using your Home Directory.
Log into your SCR Computer Labs account.
Browse to the Home Directory or H:\ drive.
Create a folder titled: public_html.
Place all images and .htm/.html files inside the public_html folder.
Make sure to name the first page or homepage index.htm.
The URL for your website will be http://complabs.nevada.edu/~username.
Substitute username for your SCR Computer Lab account username (what you use to login).
Demo philippinefamily and GIS Café email me for it Arcview list
NAME, ISBN, PURCHASED FROM
TEST ALL COMPUTERS
New data on computers
Normal progression to these topics v. cliff notes puzzle version
Samples of MP from book
Why study these issues?
Maps sharing the same coordinate systems, datum and projected the
same can align with each other.
Vs digitizing off varying data
Geodetic datums define earth’s size and shape, and thus, how best
to apply coordinate systems that will fit that surface (resulting in maps).
E.G. the right datum makes it possible to figure the elevation at a point.
If the earth was a perfect sphere, knowing the center would do what
for distance?
Knowing the shape and size also allows us to fit map projections better.
Hundreds of different datums have been used to frame position
descriptions since the first estimates of the earth's size made by Aristotle.
Remember, mapping the US we will often use the datum introduced in
1983 called the North American Datum (NAD 83) (300ft)
The U.S. military adopted much of this work but refined the values to
create the world geodetic system (WGS84).
Coordinate system
Map projection
North American datum 83
associated with this earth shape
NZ in ArcView
Absolute location is in reference to an origin or “zero point” (e.g. the
equator and prime meridian for lat/long).
To convert maps into numbers, standard ways to encode locations
as numbers are key -- these are coordinate systems.
(you can’t just say relative location, like, not far from the post office,)!
Placing the frame on the clay, so the picture/map can be hung.
Computers and plotters can understand distance from a zero point in a
x,y format (easting going east-west, northing north-south) -- this is
called a coordinate pair, put into standard coord systems.
P 47 Clarke fig. 2.11 and 2.12
Demo align vs non.
Where is the
origin or zero pt?
Four major systems
1. Geographic coordinates
2. Universal transverse Mercator (UTM) favored for many efforts
3. Military grid system (alt. Form of UTM) adopted by some countries
and used for world mapping.
4. State plane (basis of most surveying in the U.S.)
Geographic coordinates
Storage of locations as
numbers using lat/long aka
geographic cords.
This system was
standardized in 1884.
Greenwich Observatory
Demo Mt. Charleston gas stations open or closed
- add graphic over projected data
- add lat/long
- change theme name
- display by id and value 1 vs. 0
Demo
world label lat/long overlay and countries unproj
graphic to shp add xy = same
In a GIS lat and long are nearly always geocoded, or captured from the
map into the computer in 1 of 2 ways.
1. Degrees, minutes, and seconds (DMS)
2. Decimal degrees (DD)
Latitude goes from 90 degrees south (-90) to 90 degrees north (+90)
Long is the same except range is -/+180 degrees.
1 of 2 formats
1. DMS as a +/- DD.MMSS.XX here DD are degrees, MM are minutes
and SS.XX are decimal seconds. Or,
DD
DD.XXXX aka decimal degrees (like time 60 min has 60 secs)
At the equator 40,000km per 360 degrees = 111.11km, so .001 degree =
111 meters resolution (accuracy relative to perfect coastline of Africa
in fig. 2.12 in Clarke).
The major advantage to “unprojected” geographic coordinates is that
if many maps are captured the data can be transformed in a projection “on
the fly” so they overlay in whatever projection you choose.
If maps already projected are changed to GC then they could overlay.
Unprojected maps include those that are formed by considering longitude
and latitude as a simple rectangular coordinate system. Scale, distance,
area, and shape are all distorted with the distortion increasing toward poles.
Universal Transverse Mercator Coordinate System (UTM) -- included
on USGS topo maps since the late 1950s. 60 pole to pole zones, each
6 degrees of long wide, within each zone we draw a transverse
mercator projection centered on the middle of the zone oriented N-S to
form a central meridian (the equator meets it at right angles, with a
secant along 2 lines parallel to the central meridian.
For N. Hemisphere
0 northings is the equator
runs to 10,000,000 to N. Pole
(don’t use over 84 degrees)
For eastings the origin is
set at 500,000 west of the
central meridian.
We will skip the Military Grid Coordinate System
State Plane Coordinate System
You will use this often in the U.S. Used for surveying and engineering
practices (e.g. utility marking underground electric cables). A different
map exists for each state, except Alaska.
States elongated N-S (CA) drawn on a Lambert conformal conic proj.
States elongated E-W (NY) drawn on a Transverse Mercator proj.
States are then divided into as many as 5 zones to reduce distortion
better than UTM).
Each zone has an arbitrarily determined origin some number of feet west
and south of the southwestern-most point on the map (so eastings and
northings [in feet] come out as positive numbers).
Slightly more precise than UTM and so good in small areas, but lacks
UTM universality -- imagine mapping over 2 states and 2 zones, so you
would be working with 4 coordinate systems on 2 projections.
You often find grids and tic marks on maps to help for conversion into
GIS. See Clarke p 54 figure 2.18.
Points, lines and polygons (areas) can build on one another and spatial
patterns can be investigated or created only if you address these things
and mitigate things like distorting direction.
P56 Clarke Fig. 2.20.
Coordinate systems overview
http://www.colorado.edu/geography/gcraft/notes/coordsys/coordsys.html
Good sources for more information in brief text and with pictures is
http://www.lib.utexas.edu/maps/cartographic_reference.html
http://www.colorado.edu/geography/gcraft/notes/mapproj/mapproj.html
http://www.ilstu.edu/microcam/map_projections/index.html
Also has papers on various topics.
http://www.colorado.edu/geography/gcraft/notes/mapproj/mapproj_f.html
http://everest.hunter.cuny.edu/mp/
http://www.uncc.edu/~lagaro/cwg/mapproj/index.html
http://www.colorado.edu/geography/gcraft/notes/mapproj/mapproj.html#Refs
for more references
http://mcmcweb.er.usgs.gov/DSS/
Requires JAVA plug-in
* Bugayevskiy, Lev M. and John P. Snyder. 1995. Map Projections: A Reference Manual.
London: Taylor and Francis.
* Muehrcke, Phillip C. and Juliana O. Muehrcke. 1998. Map Use: Reading-AnalysisInterpretation, 4th ed. Madison, WI: JP Publications.
* Snyder, John P. 1987. Map projections: a working manual. USGS Professional Paper 1395.
Washington, DC: United States Government Printing Office.
Key terms
Use those in this lecture, no separate section in this PPT.
END
What you do on this space once you have made all the right choices
regarding what you have seen already in this PPT
Attributes of phenomena inside these spaces can be categorized by
level of measurement
1. Nominal-assign a lable or a class e.g. ski resort
2.Ordinal-rank assigned e.g. roads as trail, unsurfaced road, single ln
3.Interval-measure on a relative scale e.g. elevations on a datum
4.Ratio-measured on an absolute scale e.g. total precipitation
You can put all of these to work in GIS
Continuity refers to maps like contour maps assuming a continuous
distribution -- we discuss raster later.
Choropleth maps assume a discontinuous distribution like taxes by state