2.3 Comparison of Medium Scale and Scale Independent Soil
Mapping Procedures in Northern Thailand for Soil Data
Generation in a Development Oriented Context
For the highlands of northern Thailand, insufficient soil information is available to
support sustainable land use planning activities, with more detailed soil information
only available for the lowlands.
3 The General Soil Map of Thailand (Vijarnsorn and
Eswaran 2002) at 1:1 M scale, is so far the only map to cover the whole of northern
Thailand, but the fact that it almost exclusively represents an undifferentiated
“slope complex” (Fig. 2.6) underlines the need for more refined soil data to be
developed. Due to financial and time restrictions, comprehensive and intensive field
surveys are often difficult to achieve; hence, scale adapted and integrated mapping
strategies are usually required. In this study of northern Thailand carried out at the
landform scale (>1:100 k), soil mapping was performed based on (a) the catena
approach, (b) grid-based randomized mapping, and (c) by eliciting indigenous
knowledge. In order to assess those tools with potential for up-scaling, maximum
likelihood, classification tree and random forest algorithms were also tested, since
they are in theory scale-independent.
2.3.1 Material
Research areas: In order to cover the major lithological units of northern Thailand
as they are depicted in the medium-scale geological map (1:250,000; German
Geological Mission 1979), soil mapping was performed at the three research
sites: the Bor Krai area – which mainly consists of limestone and claystone, the
Huai Bong area – which is dominated by sandstone, and the Mae Sa (Mai) area –
which is represented by granite and gneiss.
Spatial legacy data: Digitized topographic, geological and land use maps, aerial
photographs, as well as LANDSAT and SPOT images, were used as baseline
information for the field surveys. The topographic map, as compiled by the Royal
Thai Survey Department (1976), has a scale of 1:50,000 and contour lines with
20 m intervals. This map was geo-referenced and digitized for use as a baseline. The
geological map has a scale of 1:250,000 and was compiled by the German Geological Mission (1979), while the aerial photographs have a scale of 1:15,000 and were
provided by the Military Map Department. The LANDSAT 7 ETM + image was
provided by the Global Land Cover Facility, or GLCF (GLFC 2007), and was taken
on March 5th 2000. The three SPOT 5 images were provided by Geo-Informatic
and Space Technology agency, or GISTDA (GISTDA 2007). The image covering
3 This section was prepared by Ulrich Schuler, Petra Erbe, Michael Bock, Jan Willer, Joachim
Ingwersen, Karl Stahr and Ludger Herrmann.
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
49
Mapping Procedures in Northern Thailand for Soil Data
Generation in a Development Oriented Context
For the highlands of northern Thailand, insufficient soil information is available to
support sustainable land use planning activities, with more detailed soil information
only available for the lowlands.
3 The General Soil Map of Thailand (Vijarnsorn and
Eswaran 2002) at 1:1 M scale, is so far the only map to cover the whole of northern
Thailand, but the fact that it almost exclusively represents an undifferentiated
“slope complex” (Fig. 2.6) underlines the need for more refined soil data to be
developed. Due to financial and time restrictions, comprehensive and intensive field
surveys are often difficult to achieve; hence, scale adapted and integrated mapping
strategies are usually required. In this study of northern Thailand carried out at the
landform scale (>1:100 k), soil mapping was performed based on (a) the catena
approach, (b) grid-based randomized mapping, and (c) by eliciting indigenous
knowledge. In order to assess those tools with potential for up-scaling, maximum
likelihood, classification tree and random forest algorithms were also tested, since
they are in theory scale-independent.
2.3.1 Material
Research areas: In order to cover the major lithological units of northern Thailand
as they are depicted in the medium-scale geological map (1:250,000; German
Geological Mission 1979), soil mapping was performed at the three research
sites: the Bor Krai area – which mainly consists of limestone and claystone, the
Huai Bong area – which is dominated by sandstone, and the Mae Sa (Mai) area –
which is represented by granite and gneiss.
Spatial legacy data: Digitized topographic, geological and land use maps, aerial
photographs, as well as LANDSAT and SPOT images, were used as baseline
information for the field surveys. The topographic map, as compiled by the Royal
Thai Survey Department (1976), has a scale of 1:50,000 and contour lines with
20 m intervals. This map was geo-referenced and digitized for use as a baseline. The
geological map has a scale of 1:250,000 and was compiled by the German Geological Mission (1979), while the aerial photographs have a scale of 1:15,000 and were
provided by the Military Map Department. The LANDSAT 7 ETM + image was
provided by the Global Land Cover Facility, or GLCF (GLFC 2007), and was taken
on March 5th 2000. The three SPOT 5 images were provided by Geo-Informatic
and Space Technology agency, or GISTDA (GISTDA 2007). The image covering
3 This section was prepared by Ulrich Schuler, Petra Erbe, Michael Bock, Jan Willer, Joachim
Ingwersen, Karl Stahr and Ludger Herrmann.
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
49