This document provides an overview of topographical mapping using GIS. It discusses different surface representations in ArcGIS including TIN, raster, and terrain surfaces. It compares these surfaces and describes how to analyze slopes, aspects, hillshades, and curvatures. The document outlines how to create topographical maps through contouring and defines characteristics of contours. It concludes with an assignment on preparing a topo map.

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

2. 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

3. 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.

4. 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).

5. 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.

6. 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).

7. 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.

8. 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 .

9. 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.

10. 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.

11. 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.

12. 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.

13. 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

14. 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…

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

17. Facebook Group:
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