Mapping FundamentalsMapping Fundamentals

Appendix A

Nate BowersSpring 2010

Latitude and LongitudeLatitude and Longitude

• Effective use of Lat/Long is key to making worthwhile Google Maps

• Decimal Degrees-96.01277896.012778 W

• DMS –degrees/minutes/seconds-96° 0’ 46”-96 0 4696 ° 0’ 46” W

• Recognize when a conversion needs to be made

DMS ConversionDMS Conversion• Converting from DMS to Decimal

• Converting from decimal into DMS

• Google Conversion• Online Tools

Coordinate PrecisionCoordinate Precision

Coordinate PrecisionCoordinate Precision

• Use JavaScript to maintain precision:– The toFixed built-in function “converts numbers

to strings with the given precision” (p.315).

– The toUrlValue “creates a string containing the coordinates, separated by commas and formatted with the given precision” (p.315).

Calculating DistanceCalculating Distance

• The curvature of the Earth complicates true distance. The distancefrom built-in function in JavaScript can help:

http://commons.wikimedia.org/wiki/File:Tissot_indicatrix_world_map_equirectangular_proj.svg

http://commons.wikimedia.org/wiki/File:Tissot_indicatrix_world_map_Mercator_proj.svg

EquirectangularEquirectangular

Map ProjectionsMap Projections

Map ProjectionsMap Projections

• Google Maps uses a Mercator Projection– Nothing >85° N/S– Distortion is reduced over small

latitude ranges– The higher the zoom, the lesser the

distortion• Mercator is a square map– Simplifies conversions between pixels

and Lat/Lng– Simplifies tiling

Zoom Tiles

0 1

1 4

2 16

3 64

4 256

5 1,042

6 4,096

7 16,384

8 65,536

9 262,144

10 1,048,576

11 4,194,304

12 16,777,216

13 67,108,864

14 268,435,456

15 1,073,741,824

16 4,294,967,296

17 17,179,869,184

2 miles

Sources

• Udell, Sterling. Beginning Google Maps Mashups with Mapplets, KML, and GeoRSS. 2009, New York. 313-324

• Wikipedia– http://commons.wikimedia.org/wiki/

File:Tissot_indicatrix_world_map_equirectangular_proj.svg– http://commons.wikimedia.org/wiki/

File:Tissot_indicatrix_world_map_Mercator_proj.svg

• Google Maps– http://maps.google.com