LECTURE 8: LOCATOR SERVICES, GAZETTEERS

1. THE PROBLEM

2. PLACENAMES

3. POSTCODES, AREA CODES

4. NEW GRIDS

5. GLOBAL GRIDS

The atom of geographic information

<location, time, attribute>
to communicate, we need standard ways of dealing with all three

time

Gregorian calendar
ZMT

attribute

depends on application
temperature scales
vegetation classifications
highway classifications

location

many ways of referencing

how to specify the locations of a polygon's points?

34 deg 24 min 42.7 seconds North, 119 deg 52 min 14.4 sec West
909 West Campus Lane, Goleta, CA 93117, USA
3811560N, 236150E, Zone 11, Northern Hemisphere
NE 1/4, Section 12, Township 23 Range 5 of the Second Principal Meridian
National Grid reference 11SKU36151156
Mike Goodchild's house

uniquely, so there is no confusion
in a way that others can understand
with sufficient accuracy for the application

many methods

can they be converted?

are they interoperable?

georeferencing
geocoding
geolocating

within the geographic frame of reference

other frames of reference?

uniqueness

one code per location
every location gets its own code

over what domain?

the entire globe
universal systems
latitude/longitude

over a limited domain

e.g. unique in the U.S.
e.g. unique to a UTM zone
e.g. unique to my farm

same geocode repeats in different places

7-digit phone number repeats in every area code
10-digit phone number unique in the U.S., Canada, parts of the Caribbean
11-digit phone number (add 1) unique in the world

UTM coordinate repeats 120 times

placenames repeat

at least 18 states have a city of Springfield

"an old sycamore tree" is not unique

note the indefinite article

"the old sycamore tree" may be unique to a property

shared meaning

sender and receiver must both understand
latitude/longitude is universally understood

so is mailing address

another postcard

persistent through time

latitude/longitude since the 1890s

but datum varies

area codes often change

ZIPs sometimes do

spatial resolution

how big is the area covered by a single georeference?

Rhode Island pins location down to 3000 sq km
California only to 410,000 sq km

area or linear measure?

a square of 3000 sq km is about 55 km across
a square of 410,000 sq km is about 650 km across
we tend to work with both

metric georeferences

measure position with respect to fixed points
can be used to measure distances between points

coordinates
e.g. Salt Lake City street addresses

800 ft per block, 8 ft per address

if you live at 450 on N 1300 W St your house will be almost exactly 10400 ft W and 3600 ft N of Main and S Temple

ordered allocation

e.g. New York avenues

a method for finding location on the Earth's surface

Locations identified by name

likely the first type of georeference

littering the surface of the Earth

Placename authorities

state, national boards
official authorization

Board on Geographic Names
Geographic Names Information System
Alexandria Digital Library Gazetteer
www.geonames.org

e.g. 5 miles west of Greenfield, CA
e.g. between Salinas and Greenfield

the museum collection problem

collected 1 mile north of Cachuma Saddle

metes and bounds property description

from the big maple tree, 100 ft in a southerly direction to the crossing of the creek

variable spatial resolution

e.g. Asia
e.g. Eiffel Tower

lost or change through time

where was Camelot?
where was Saigon?
placenames of medieval China

only locally defined

the Riviera
downtown
the tricounties

not officially recognized

the Midwest

fuzzy or crisp

the Atlantic Ocean

context-specific

LA

if you live in New York
if you live in Riverside

alphabets

Chinese placenames
diacritical marks

an index linking placenames (and domains) to coordinates
intersection

the vague world of human language
the precise world of GIS

most people don't know their coordinates

gazetteer service

a service that replaces placenames with coordinates

gazetteer

a relation linking placenames to coordinates

with feature extent

who's asking?

Google in India and China

point-of-interest database

businesses, prominent features

geoparsing

mining text for placenames

Metacarta

Wiki efforts to build gazetteers

Wikimapia

microformat

geotagging

adding coded tags to pages

e.g. Wikipedia entries

e.g. photos in flickr

Devised for specific purposes

used for many other purposes

ZIP - 93117-4338

unique in US
spatial resolution <1 block
changes made frequently
UK postcode - SE3R 1KW

Canadian postcode - N6G 1R1

widely known and accessible

mailing lists
widely used for marketing, analysis

Area codes

useful as geocodes?

905

4. NEW GRIDS

Lat/long is cumbersome

DMS
left-most digits redundant for most people

The National Grid

an effort to establish a single easily used grid for the US

US National Grid

a single string of characters

18SUJ20 - locates a point with a precision of 10 km

18SUJ2306 - locates a point with a precision of 1 km

18SUJ234064 - locates a point with a precision of 100 meters

18SUJ23480647 - locates a point with a precision of 10 meters

18SUJ2348306479 - locates a point with a precision of 1 meter

length determines spatial resolution

based on UTM

2 digit zone number

1 letter 8-degree latitude range

1 letter 100km N-S

1 letter 100km E-W

decimal digits northing

decimal digits easting

e.g. my house 34 24 42.7 N, 119 52 14.4 W

11SKU3614611561

UTM Zone 11 236146m East, 3811561m North

The GO2 grid

general principles, details may vary

city-centered

e.g. Santa Barbara Courthouse
e.g. LA Courthouse
e.g. Washington Monument

"stake hammered into the ground"

stereographic projection also centered

100 km square centered

most city residents and visitors live and work in this area

first level - 10 km resolution

number columns 0 thru 9
number rows 0 thru 9

pair of digits gives location to 10km resolution

second level - 1 km resolution
third level - 100 m resolution
fourth level - 10 m resolution

interleave digits, separate by periods

e.g. 34.71.84.06

is 37800 m east, 41460 m north
rounded to nearest 10 m

city center is at 55.55.55.55

looks like an IP address
combine with city ID

e.g. SBA.34.71.84.06

a grid that is Internet-ready

How to reference the entire globe

without projection distortions

Perspective Orthographic projection

without interruption at the poles and dateline

with smooth zoom to local scales

virtual globes

Implementations

Google Earth

Microsoft Bing Maps

NASA World Wind

Dutton's Quaternary Triangular Mesh (QTM)

indexing scheme

Level 0 - 0 thru 7
Levels 1... - 0 thru 3

e.g. 6310132

references about 1/(8x4x4x4x4x4x4) of the Earth's surface
or about 15,300 sq km

level 13 is 1 km resolution

Colorado State's Icosahedron grid

Geofusion/ArcGlobe grid

rendered

3D solid-Earth grid