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# Comparing directional maps

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Presented in AAG 2008. Boston

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### Comparing directional maps

1. 1. Rahul Rakshit PhD Candidate Clark University [email_address]
2. 2. Major Points
3. 3.
4. 4. http://weather.gfc.state.ga.us/Maps
5. 5. http://ipf.ov.ingv.it/MorphoVesuvio_file/Gallery/Ves_Gallery.htm
6. 6. Location: Plum Island Ecosystems Long Term Ecological Research (LTER) site
7. 7.
8. 8. Queen’s Case Rooks' Case
9. 9. ArcGIS Aspect Values (Degrees) Idrisi Aspect Values (Degrees) Scatterplot: Resolution 30 m
10. 10. Issue in comparing directions Aspect is a circular variable All the Units are in Degrees 360 90 180 270 5 355 10 350
11. 11. Fine Resolution Coarse Resolution Vector Addition: To coarsen the resolution Direction 0 270 90 225 Direction 37 Magnitude 5 Magnitude 6 2 7 2√2 2 North 6 2√2 5 resultant 37˚ 7
12. 12. :90 00 :90 00
13. 13. Coarse Resolution Aspect Maps After Vector Addition
14. 14. Scatter Plots: X Axis ArcGIS – Y Axis Idrisi
15. 15. Resolution (m) MAE (Degrees) Mean Absolute Error (MAE) Shows the average difference in direction Coarse Fine MAE is the weighted average of absolute errors
16. 16. Major Points
17. 17. <ul><li>For more information, please contact at : [email_address] </li></ul><ul><li>To tackle other types of variables, read the following from www.clarku.edu/~rpontius: </li></ul><ul><ul><li>Pontius, Thontteh and Chen. 2006. Components of information for multiple resolution comparison between maps that share a real variable. Environmental and Ecological Statistics. </li></ul></ul><ul><ul><li>Pontius and Cheuk. 2006. A generalized cross-tabulation matrix to compare soft-classified maps at multiple resolutions. International Journal of Geographical Information Science. </li></ul></ul><ul><li>Rahul extends special thanks to: </li></ul><ul><li>Prof. Robert Gilmore Pontius Jr. for the concept and advice in every step of </li></ul><ul><li>this research. </li></ul>Acknowledgements and Plugs
18. 18. Aspect ArcGIS (Radians) Aspect Idrisi (Radians) Cos (Aspect) Sin (Aspect) Cos (aspect) Sin (Aspect) Slope (ArcGIS) Slope * Sin Slope * Cos Aggregate to coarser resolution Vector Addition (ArcGIS) Slope (Idrisi) Slope * Sin Slope * Cos Aggregate to coarser resolution Vector Addition (Idrisi) Scatter Plots at Coarser Resolutions Study Area Mask Mean Absolute Error (MAE) Elevation Coarse Angle(ArcGIS) Coarse Angle(Idrisi) Coarse Angle Difference