Surface Representations using GIS AND Topographical Mapping

Topographical Mapping using GIS
GIS Training : Day 11,12 @IOE, Pulchowk

Presentation Outline
Surface Representation in Arc GIS
TIN, Raster and Terrain Surfaces
Comparison between Surfaces
Analyzing Surfaces:
Slope, Aspect, Hillshade and Curvature
Topographical Mapping
Contouring
Characteristics of Contours
Preparing a topo map: Assignment

Surface representation in ArcGIS
A 3D Surface model is a digital representation of features, either
real or hypothetical, in three-dimensional space.
They are usually derived, or calculated, using specially designed
algorithms that sample point, line, or polygon data and convert it
into a digital 3D surface.
 ArcGIS can create and store three types of surface models: TIN,
Raster, and Terrain dataset.

Contd…
With ArcGIS, there are two approaches for managing your surface
data: geodatabase or file-based.
Choice of the surface is partially your choice but is also limited by
the surface type.
Geodatabases are collections of spatial data native to ArcGIS that
collate several features or raster datasets all in one place.
File-based formats can be ESRI specific (TIN, GRID), open-source and
standardized exchange formats (TIFF, JPEG), or third-party formats
(IMG, PIX).

Triangulated Irregular Network (TIN)
TINs are a form of vector-based digital geographic data constructed by
triangulating a set of vertices (points).
ArcGIS supports the Delaunay triangulation method.
Delaunay triangle criterion ensures that no vertex lies within the
interior of any of the circumcircles of the triangles in the network.
If Delaunay criterion is satisfied everywhere, the minimum interior
angle of all triangles is maximized.
TINs cannot be stored in any of the three types of geodatabases; they
can only be stored in file-based storage solutions.

Raster Surfaces
Raster surface data represents a surface as a grid of equally sized cells
that contain the attribute values for representing the z-value and the
x,y location coordinates.
 Each cell represents a defined square area on the earth's surface and
holds a value that is static across the entire cell.
Elevation models are one such example of raster surface models.
 The fixed point may be a spot height derived from
photogrammetric methods, but interpolation between heights
help form the digital elevation model (DEM).

Terrain Surfaces
Terrain datasets are an efficient way to manage large point-based data
in a geodatabase and produce high-quality, accurate surfaces on the
fly.
A terrain dataset in the geodatabase It doesn't actually store a surface
as a raster or TIN. Rather, it references the original feature classes.
This organization involves the creation of terrain "pyramids" that are
used to quickly retrieve only the data necessary to construct a surface.
Can be stored in a personal, file, or multiuser geodatabase.

Comparison between Surfaces
TIN models are less widely available than raster surface models and
tend to be more time consuming to build and process.
The cost of obtaining good source data can be high, and processing
TINs tends to be less efficient than processing raster data because of
the complex data structure.
TINs are typically used for high-precision modeling of smaller areas,
such as in engineering applications, where they are useful because
they allow calculations of plan metric area, surface area, and volume.
Terrain datasets and related tools offer benefits in the areas of data
management, analysis, and visualization in case of voluminous data .

Analyzing Surfaces
Surface analysis involves several kinds of processing, including
extracting new surfaces from existing surfaces, reclassifying
surfaces, and combining surfaces.
Most common Terrain analysis tools: Slope, Aspect, Hillshade,
and Curvature tools.

Slope ,Aspect, Hillshade and Curvature
The Slope tool calculates the maximum
rate of change from a cell to its
neighbors, which is typically used to
indicate the steepness of terrain.
The Aspect tool calculates the direction
in which the plane fitted to the slope
faces for each cell.

Hillshade shows the intensity of lighting
on a surface given a light source at a
particular location
It can model which parts of a
surface would be shadowed by
other parts.
Curvature (the second derivative of the
surface) calculates the slope of the slope
and finds out whether a given part of a
surface is convex or concave.
Convex parts of surfaces, like ridges,
are generally exposed and drain to
other areas.
Concave parts of surfaces, like
channels, are generally more
sheltered and accept drainage from
other areas.

Topographical Maps
Type of maps in which the configuration of the terrain along with
the horizontal position of the natural and artificial features above
the given terrain is represented.
Topographic maps are also commonly called contour maps or
topo maps.
The various features shown on the map are represented by
conventional signs or symbols. For example, colors can be used to
indicate a classification of roads.

Contouring
General definition:
A Contour line (also isoline, isopleth, or isarithm) of a
function of two variables is a curve along which the function
has a constant value.
It is a cross-section of the three-dimensional graph of the
function f(x, y) parallel to the x, y plane.
In Surveying and mapping , Contours are the imaginary lines that
connects the points of equal elevation.
Contour interval of a contour map is the difference in elevation
between successive contour lines.
Types: Index and Intermediate Contours
Usually every fifth contour line is shown in a heavy, wider line,
so called an index contour

Characteristics of Contours
 The contour are closed curves.
Contour line do not cross to each other.
Important points can be further defined by including a “spot”
elevation.
Contour line cross valley lines at right angles.
Contour line cross ridge line at right angle. The contour line form
U shaped curve.
Ridge contours can be confused with valley contours as they, too, form
'U' shapes - the difference is that the closed end of the 'U' points to
lower ground.
 Depression and hill look the same.
And Many more…

Surface Representations using GIS AND Topographical Mapping

Prepare a Topo Map - Assignment
1. Datasets Location:../day11-12/road_details.csv
2. Manual document -See the pdf: Prepare_map.pdf

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Surface Representations using GIS AND Topographical Mapping

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Surface Representations using GIS AND Topographical Mapping