georeferencing with paper maps map basics how to georeferencing with paper maps latitude and...

Georeferencing with Paper Maps

Map Basics

How to Georeferencing with Paper Maps Latitude and Longitude Mathematically Error Calculator

(pay attention, you are doing this next!)

Pros and Cons of Paper Maps

Pros 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 Time-consuming Good quality paper maps may be hard to find Map printing errors

Map of Canada’s Wonderland, N of Toronto, Canada

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Map Basics

Projection

Map Anatomy: Scale Graticule Datum

Citing Map as Georeferencing Source

Projection

Map projection is about rendering 3D into 2D. Map projection is about compromises in order to preserve either area, linear distance or shape.  

Which compromise is right for the map? 

ProjectionGeographicpreserves NS distance

Mercatorpreserves shape (terrible for

poles, distorts area)

Projection

Winkel Tripel (NGS solution)reduced distortion in both area and distance

Projection“Butterfly” map – Cahill 1909• emphasis on symmetry• preserves area, shape• contiguous land masses

Projection: Regional

Squat California (Geographic) vs. Equal-Area California (Teale Albers)

The Paper Map

Map Anatomy: Map Scale

HeaderHeader

Map Anatomy: Map Scale

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. Example 1/10,000 > 1/500,000

Map Anatomy: Map Scale 1:25,000 Large Scale

Map Anatomy: Map Scale 1:250,000Smaller 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

Map with no grid labeled

Map Anatomy: Grid

Shows the placement of the parallels and meridians on maps

Used to determine latitude and longitude Maps with graticule cannot be used to determine

coordinates – only to determine extents Can have more than one grid system in place (e.g.,

easting and northings for UTM and latitude and longitude)

Universal Transverse Mercator

The Grid/ Graticule

UTMNorthings

UTMEastings

Map Anatomy: Datum

Map with no grid labeled

Map Anatomy: Datum

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://earth-info.nga.mil/GandG/publications/tr8350.2/wgs84fin.pdf (Use Appendix B)

Determining Coordinates from Paper Maps: Georeferencing Source For Georeferencing Sources be sure to

include the following: Publisher name Map Date Map Scale Map name

Example: USGS 15’ Topographic Series Boone 1956 or

USGS Topoquad 1:24000 Key West 1962

Determining Coordinates from Paper Maps

Paper maps are necessary when gazetteers will not report needed coordinates 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) when reporting in decimal degrees

Coordinate Integers for Hemispheres

Determining Coordinates from Paper Maps

Nauru Island, Pacific Islands Geographic Nauru Island, Pacific Islands Geographic

Society, 1960 1:12,000Society, 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:Determining Coordinate Precision for the Georeferencing Calculator:

The smallest measurement using our rulers is 1 mm ( = 0.1 cm), The smallest measurement using our rulers is 1 mm ( = 0.1 cm), therefore we need to convert millimeters to minutes:therefore we need to convert millimeters to minutes:

0.1 cm x (2 minutes/14 cm) = 0.014 min0.1 cm x (2 minutes/14 cm) = 0.014 min

Choose the next largest fraction of a minute on the calculator.Choose the next largest fraction of a minute on the calculator.

For 0.014 minutes, select 0.1 minutes.For 0.014 minutes, select 0.1 minutes.

Determining Coordinates from Paper Maps: Error Calculation

In Conclusion 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

For Georeferencing Source be sure to include the following: 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 Lat and Long:Determining Lat and Long:

Determining Coordinate Determining Coordinate Precision:Precision:

0.1 cm x (2 minutes/14 cm) = 0.014 min0.1 cm x (2 minutes/14 cm) = 0.014 min

Round up to 0.1 minute precisionRound up to 0.1 minute precision

Determining Coordinates Using the Error Calculator

Latitude Increases

Longitude Increases

Find a set of coordinates on the map from which lat and long increase. This is your “starting point”

Measure orthogonal offsets from these coordinates

Use calculator to determine “end point” coordinates

Use the calculator a second time for the error calculation

Measuring Orthogonal Offsets from Grid

Coordinates

Measure distance east of longitude grid line.

Measure distance south of latitude grid line.

Determining Coordinates

Determining Coordinates

Error Calculation