1. Talking
With Maps
2010
Imaging of geochemical data
by interpolation within
geological boundaries
Don Appleton
(British Geological Survey)
Presented by Claire McGinn
(Geological Survey of Northern Ireland)
2. Talking
With Maps Acknowledgements
2010
This work is based on research using a
VB.Net tool compiled for ArcGIS 9.3 by Keith
Adlam (BGS)
Data for this work were provided by the Tellus
Project, funded by the Department of
Enterprise, Trade and Investment of Northern
Ireland.
The contributions of GSNI and BGS staff who
collected, prepared and analysed the Tellus
soil samples is gratefully acknowledged.
3. Talking Northern Ireland
With Maps
2010
Area: 14,000km2
19. Talking
With Maps
2010
Step 1: Geology polygons are intersected with the 1km Grid
Step 2: Centroids are created for each geological polygon within
each 1km polygon
Step 3: VB.Net Tool identifies the nearest 5 soil sites to the centroid
for the Parent material and superficial geology
20. Talking Sample points
With Maps and centroids
2010
(Parent material
method )
Rasterised image
of the centroids
interpolated
within parent
material
boundaries
21. Chromium in soils
Talking
With Maps
2010 New Parent
Material mapping
Old method using
IDW mapping.
22. Parent Material soil chemistry maps:
Talking optimum number of samples for Parent
With Maps
2010
Material mapping
2
1 n
MSD = ∑ (estimated − measured )
n i =1
1.8
As AV
1.6 Cr AV
Ni AV
1.4 Pb AV
Average of As, Cr, Ni, Pb AV
Overall average ALR-GALA
1.2
1
MSD
0.8
0.6
0.4
0.2
0
0 5 10 15 20 25
Number of neighbouring samples
23. Evaluation of Parent Material and IDW
Talking
soil chemistry mapping using holdout
With Maps
2010 validation
Mean squared deviation (MSD) for As, Cr and Pb for the
three mapping methods based on combining the results
for two 10% holdout subsets. Lowest MSD values for
each element indicated in bold type. (Lne data).
2
1 n
MSD = ∑ (estimated − measured )
n i =1
Element Spatial Parent Parent
analyst Material Material
IDW mapping mapping
(GM) (IDW GM)
As 0.18 0.15 0.16
Cr 0.43 0.31 0.31
Pb 0.20 0.19 0.21
24. Chromium in
Talking
soils – all NI
With Maps
2010
New regional
Parent
Material
mapping.
Old version
using IDW
