Transcript Georeferencing with paper maps – Workshop guide

Georeferencing with Paper
Maps
Museum of Vertebrate Zoology
University of California, Berkeley
& Royal Ontario Museum, Toronto
Overview
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Map Anatomy
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Scale
Grid
Datum
Publisher
Georeferencing with Paper Maps
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Latitude and Longitude Mathematically
Error Calculator
Pros and Cons of Paper Maps
Pros of Paper Maps
 Necessary for certain localities, such as distances by road and
topographic features, especially when GIS layers are not readily
available
 Extents more readily obtained
 Old paper maps may be the only option for obtaining coordinates
for historic localities
Cons of Paper Maps
 Time-consuming
 Good quality paper maps may be hard to find
 Map printing errors
Map of Canada’s Wonderland, N of
Toronto, Canada
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Map Anatomy: Map Scale
Map Anatomy: Map Scale
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Usually recorded as a ratio, such as
1:100,000, or a fraction, such as 1/100:000
“Large scale” (Fine scale) maps, such as
1/10,000, show finer detail, less area
“Small scale” (Broad scale) maps, such as
1/500,000, show less detail, greater area
Think of “large” & “small” scale as the value
of 1 in the fraction.
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Example 1/10,000 > 1/500,000
Map Anatomy: Map Scale 1:25,000 Large Scale
Map Anatomy: Map Scale 1:250,000
Smaller Scale
Map Anatomy: Map Scale 1:500,000
Smaller than before
Map Anatomy: Map Scale 1:1,000,000 Small Scale
smaller than before
Map Anatomy: Grid
Map Anatomy: Grid
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Shows the placement of the parallels and
meridians on maps
Used to determine latitude and longitude
Maps with no grid recorded cannot be used
to determine coordinates – only to determine
extents
Map Anatomy: Grid
Map with no grid labeled
Map Anatomy: Datum
Map with no grid labeled
Map Anatomy: Datum
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If datum is recorded, usually found near the
map scale or publisher’s name
Use Horizontal Datum, not Vertical
Occasionally, if no datum is recorded but the
reference ellipsoid is, then one can determine
the datum using the pdf document found at
http://earthinfo.nga.mil/GandG/publications/tr8350.2/wgs
84fin.pdf (Use Appendix B)
Determining Coordinates from Paper
Maps: Georeferencing Source
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For Georeferencing Sources be sure to
include the following:
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Publisher name
Map Date
Map Scale
Map name
Example: United States Geological Society
(USGS) Topographic Map California, 1956,
map scale 1:24,000, map name “Boone”
Determining Coordinates from Paper
Maps
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Paper maps are necessary when gazetteers
will not report needed coordinates
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Especially useful for distances by roads and
topographic features like rivers and mountain
ranges
Pay special attention to the grid lines and the
hemisphere (latitudes in the southern
hemisphere are negative, and longitudes in
the western hemisphere are negative)
Coordinate Integers for Hemispheres
Determining Coordinates from Paper Maps
Nauru Island, Pacific Islands Geographic
Society, 1960 1:12,000
Determining Coordinates from Paper Maps: Latitude
Determining Coordinates from Paper Maps: Latitude
S
Determining Coordinates from Paper Maps: Longitude
Determining Coordinates from Paper Maps: Longitude
E
Determining Coordinate Precision
Determining Coordinate Precision for the Georeferencing Calculator:
The smallest measurement using our rulers is 1 mm ( = 0.01 cm),
therefore we need to convert millimeters to minutes:
0.1 cm x (2 minutes/14 cm) = 0.014 min
Choose the next largest fraction of a minute on the calculator.
For 0.014 minutes, select 0.1 minutes.
Determining Coordinates from Paper Maps: Error Calculation
In Conclusion
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Pay attention to whether you should add or
subtract the offsets to the grid points
Measure from the center of your feature to
the edge for extent
Plot your coordinates to double check your
work
Explain any decisions you had to make in the
GeoreferenceRemark field
Explain any errors in the locality description
in the LocalityErrors field
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For Georeferencing Source be sure to include the following:
 Publisher name
 Map Date
 Map Scale
 Map name
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Example: United States Geological Society (USGS) Topographic Map California, 1956,
map scale 1:24,000, map name “Boone”
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Determining Lat and Long:
Determining Coordinate
Precision:
0.1 cm x (2 minutes/14 cm) = 0.014 min
Round up to 0.1 minute precision