### Using Google Earth to Measure Positions and Distances Geog 366 Observation Assignment

OBJECTIVE: The primary objective is to gain familiarity with imagery, coordinates and distances in Honolulu's geography. A secondary objective is to get an idea of your "foot-print" in the city. A tertiary objective is to think about whether Honolulu is "Cartesian", i.e. does the Pythagorean formula describe our travel experience, or is another metric more appropriate?

Google Earth is an interesting resource for getting a quick image-based geographic overview, a modern, web-dependent, high-tech version of the "trusty old" map or aerial photograph. You will use Google Earth to determine coordinates for several places, the distances between them (measured several ways), and compare those measures to see how physical and experienced distances are related in Honolulu. (If you do not have access to it on a computer of your own, we can arrange access via one of the university's computer labs.)

USING GOOGLE EARTH: Using Google Earth, it becomes easy to determine and record geographic coordinates, and to measure distances and the lengths of the routes between points. (I hope that you'll enjoy usng this tool and will find it helpful this term. Take a little time to become familiar with it.)

Set up.
Tools : options : 3D View tab... Show Lat/Lon as decimal degrees. Show elevation in meters, and distances in kilometers,.
View : check "Status Bar".

Location of the pointer (hand) is displayed in the Status Bar as decimal degrees of latitude and longitude and meters of elevation. (You could transcribe these from there.)

Push-pin (placemarker), Polygon, and Path Tools. Click the tool. Enter a mnemonic name. Set style and color. Digitize. (finally) click "OK" to close the panel. (You can reset the "properties" of a placemarker, polygon or path; right-click its name in the sidebar.)

Ruler (measurement) Tool. Set the units (meters). Select (straight) line or path (multiple segments) length. Click along the path or line. Read the result from the panel.

You can save the image (including your digitized paths) as a 'jpg' file. File : Save : Save Image...

You can save the coordinates of your push-pins and paths to a .kml file: In the sidebar, under the "Places" tab, Right-click the "My Places" (or "Temporary Places") line and select "Save as..." from the drop-down menu. Enter a filename (like, your initials + "-366.kml"). KML is a little verbose, but you can fine the coordinates among the txt.

Locate your home, this classroom, a friend's home, your job (or a recreation site), and a grocery store near your home in Google Earth. Record the coordinates as decimal degrees (not degrees, minutes, decimal seconds) of latitude and longitude in a table like the one below.

Digitize the paths that you usually take between home and each of these sites using the "add path" tool, giving each a suitable mnemonic name.

Save a "jpg" image showing your "foot print" in Honolulu. Call the file "366-footprint-your initials .jpg" .

Measure the straight-line and path distances between your home and your distinations using the "ruler" tool (in kilometers). (Sorry to ask you to re-trace the paths that you just entered; does anyone see a way to get the path length from the paths automatically?) Enter these distances in the table.

Estimate, from your experience, how long each of these trips takes (in minutes) and enter these in the table along with the transport mode (walk, car/motorcycle, bus, bike, etc) that you use for the trip. (Time is often used as a surrogate for distance, as in: "My apartment is only 15 minutes to the beach."

Sketch scatter plots of
(a) path distance (y axiz) against straight line distance (x axis), and
(b) travel time (y axis) against straight line distance (x axis), like below.

### THE REPORT:

Include the following table (with values filled-in):
Place Latitude (dd) Longitude (dd) Dist-to-home (km) Path-to-home (km) Time-to-home (min) Transport Mode
Home     0.00 0.00 0.00 none
Classroom
Friend
Job/Rec
Grocery

Include your "footprint image" (the jpg image of your places and routes) (if possible).

Write a description (one page max + table + graphs) of the relationships you note between travel time, path length, and straight line distance. Are these metrics getting at the same thing? Which is the 'best'? Why (i.e., for what)? Do transport mode, length of trip, or other factors matter in that choice? Along the way, indicate how you estimated your travel times, and note the "mode(s) of transport" that you use/assumed when estimating the times. Finally, do distances getting around Honolulu work like it is a Cartesian space? Why/why not.

### Food for Thought

How does Google Earth measure distance? I.e., given two latitude-longitude pairs (and paths are just more of these strung together) does Google Earth:

• calculate the arc between the points with spherical trigonometry and multiply by a scale factor to get a linear distance?
• work in map projected (flat) space and calculate the distance with:
d = ((X1-X2)^2 + (Y1-Y2)^2 )^0.5 ?
• work out a geodesic on the terrain surface model in its database?
• look it up in a database of all inter-point distances>
• some other strategy?
How could you tell which?

Even deeper... How should one measure distance in Honolulu? Should the measure include the constraints of street networks? the effects of topography? the mode of transport? the time of day?

### Some References:

Krause, Eugene F. 1975. Taxicab Geometry: An Adventure in Non-Euclidean Geometry. Addison-Wesley. Menlo Park, CA.

Ellis, George F. R. and Williams Ruth M. 1988. Flat and Curved Space-Times. Clarendon Press. Oxford. [Hamilton QC 173.65 .E45 1988]

Smart, J. J. 1964. Problems of Space and Time. Macmillan. New York.

Wood, Denis. 1978. "Introducing the Cartography of Reality", Chapter 13 in David Ley and Marwyn S. Samuels (editors), Humanistic Geography: Prospects and Problems. Maaroufa Press. Chicago.

Pau.