This presentation discuss about Arc Geographic Information System (GIS) Digital Elevation Models (DEM). DEM data sources.

1. Emergency Response Management: Principals and
Practices
DM 5233
Presentation on
ArcGIS DEM
By
Uday Kumar Shil
1350
Department of Geography and Environment
University of Dhaka
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2. Introduction
GIS: A geographic information system
(GIS) is a computer system for
capturing, storing, checking, and
displaying data related to positions
on Earth’s surface. GIS can show
many different kinds of data on one
map. This enables people to more
easily see, analyze, and understand
patterns and relationships. The
definition of GIS is not that important
but it must encompass.
• Data & concepts concerned with
spatial distribution (Geographical)
• Notion of conveying data, ideas or
analysis (Information)
• Sequence of inputs, processes &
outputs (System)
Source: NATIONAL GEOGRAPHI
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3. Digital Elevation Models (DEM)
A Digital Elevation Model (DEM), also referred to as the
Digital Terrain Model (DTM) is a digital representation of
earth's topography, i.e. an elevation map. DEMs can be
used to derive topographic attributes, geomorphometric
parameters, morphometric variables or terrain information
in general. In combination with other spatial data, digital
elevation models are an important database for
topography-related
analyses or 3D video
animations
(e.g. fly-throughs). Different
georeferenced 3D products can be derived and
complemented by a coordinate system and presented in a
2D-map projection or as a 3D perspective view.
Source: GISGeography
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4. Cont…
• In order to avoid confusion of terminology, we use the
term DTM to describe a set of interpolation/filtering
techniques used to derive the topographic surface, and
the term DTA for a set of techniques used to derive
terrain parameters. The following terminology is
commonly used:
• DEM – Digital elevation map, i.e. representation of the
Earth's surface topography
• DTM – a set of techniques used to derive or present a
DEM
• DEM filtering – a set of techniques used to improve the
geomorphic resemblance of a DEM
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5. DEM data sources
At present, there are five main sources of the elevation data:
1. Ground surveys;
2. Airborne photogrammetric data capture;
3. Existing cartographic surveys (e.g. topographic maps);
4. Airborne laser scanning and
5. Stereoscopic or radar-based satellite imagery.
These DEM collection methods can be compared considering four aspects:
(a) price
(b) accuracy
(c) sampling density and
(d) pre-processing requirements
Traditionally, elevation data has been collected by land-surveyors from
ground surveys or by semi-automated digitizing using stereoplotters. This is
the most accurate but also the most expensive data collection method.
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6. DEM data structures
In a GIS environment, a DEM is commonly
modeled and visualized using two main data
structures:
1. Rectangular grid or elevation matrix
(GRID) and
2. Triangulated Irregular Network (TIN).
Exact information about the Earth’s surface is of
fundamental importance in all geosciences. Topography
exerts control over range of Earth surface processes
(evaporation, water flow, mass movement, forest fires)
which are important for energy exchange between the
physical climate system in the atmosphere and the
biogeochemical cycles at the Earth surface.
Geological Applications of DEMs
GRID TIN
Source: NCGIA
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7. Applications in Topographic Studies
Topography is a graphic representation of natural
features of the earth's surface including hills,
valleys, rivers, lakes and other similar features.
Typically, topography is drawn on maps and charts
or as shaded relief.
DEMs have many applications in remote sensing
and mapping, such as topographic mapping
(contours), thematic mapping, orthoimage
generation and image analysis, map revision,
and so on.
Applications in Remote Sensing and Topographic Mapping
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8. Use of DEMs in Geological Mapping
DEMs are important in providing valuable geological information that can be used as a
guide in defining the geology of a given area. The following functions have been found
to be most useful in depicting geological information:
1. Slope 2. Aspect 3. Shaded topographic relief or hill-shading 4. Flow direction
5. Basin
Applications in Mineral Exploration & Water Resources
Digital elevation models deliver basic information on geologic
structures. These information sources are especially important in
remote areas where coverage by topographic maps is limited.
Exploration geologists are possibly the most experienced users of
digital elevation models and multipectral remote sensing data. By
analyzing digital elevation models they determine promising
regions of potential mineral deposits which find an expression as
a topographic prominence or depresion, or placer deposits found
along stream channel.
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9. Reference
NATIONALGEOGRAPHI. “GIS (geographic information system)”. [Online]
https://www.nationalgeographic.org/encyclopedia/geographic-information-system-gis/
Department of Geology. Aligarh Muslim University. “Digital Elevation Models & their Applications
in Geological Studies”. [Online] http://www.geol-amu.org/notes/rs12-4-1.htm
GIS Geography. “Global DEM Data Sources – Digital Elevation Models”. [Online]
https://gisgeography.com/free-global-dem-data-sources/
Hengl, T., Gruber, S. and Shrestha, D.P. (2003). “DIGITAL TERRAIN ANALYSIS IN ILWIS”. P. 4 [Online]
https://webapps.itc.utwente.nl/librarywww/papers_2003/misca/hengl_digital.pdf
Bitters, Barry. NCGIA. “Terrain Data”. Unit 6 [Online]
http://ncgia.ucsb.edu/cctp/units/unit06/06_f.html
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