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Topographic Base Map Update in Nepal: A Preliminary Update on Challenges and
Article · January 2021
3 authors:
Pratik Dhungana
Nimisha Wagle
Survey Department, Nepal
Brown University
Tri Dev Acharya
University of California, Davis
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Landslide Susceptibility Mapping of Sindhupalchowk, Nepal View project
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Survey Department, Government of Nepal, Minbhawan, Kathmandu, Nepal
School of Geomatics and Urban Spatial Information, Beijing University of Civil Engineering
and Architecture, Beijing 102616, China
Institute of Transportation Studies, University of California Davis, Davis, CA 95616, USA
Pratik Dhungana (1),
Nimisha Wagle (1),
Tri Dev Acharya (2,3)
Email: pratik.tan10@gmail.com; wagle1996@gmail.com; tridevacharya@gmail.com
Topographic Base Maps (TBMs) are essential for
any development project as the planning of such
a project begins by desk study of the required area
using topographic maps. Thus, to help make the best
possible plans and decisions, TBMs must show the true
and current ground reality. This necessitates periodic
updating of these maps. In Nepal, Survey Department
(SD) being the only National Mapping Organization
has been updating TBMs of Nepal since 2004 and is
providing updated digital databases as well. Realizing
the demand for updated data, since 2018 SD has been
updating more than 200 sheets per year in contrast
to around 10 sheets per year in the past. This huge
jump in rate is a necessary step to ensure the most
up-to-date representation of topographic, natural
and manmade features on the base map. However, it
has faced many challenges, mainly due to difficult
terrain, lack of accessibility, lack of sufficient welltrained manpower, the incompleteness of existing
guidelines and specifications and mostly due to lack
of proper planning. Learning from experience, many
problems have been resolved and some innovations
have been introduced to minimize the burden on
working manpower and to avoid the introduction of
errors at various stages. This paper presents various
challenges faced during various stages of the TBM
update program along with ways in which they were
resolved. It also recommends possible innovative
ways to further improve the quality of the output
Key Words
Topographic Base Map, Survey Department, Nepal,
Challenges, Solutions
along with minimizing wastage of human efforts and
Broadly, a Topographic Map (TM) is a 2-D
representation of the earth’s 3D landscape, where
details of topography, artificial and natural features
are accurately represented (Menno-Jan & Ormeling,
2011). A base map is a map showing features of
different themes and thus serves as a base to derive
various thematic maps (Government of Canada), 2011).
A base map is generally produced and maintained
by the National Mapping Organization (NMO) of a
country. In Nepal, the only NMO of the country is
The Survey Department (SD) and TM of scale 1:2500
and 1:50000 prepared from 1991 to 2001 serve as
the base map of the country. Topographic Survey
and Land Management Division of the department
is responsible for the preparation, maintenance,
updating & distribution of the Topographic Base Maps
(TBMs) of Nepal whereas digital data is disseminated
by Geographic Information Infrastructure Division
(GIID) (Shrestha, 2009).
TBMs of Nepal were prepared at various scales by
different agencies. Firstly in 1930, 1 inch to 4- mile
scale 26 TBM sheets covering the whole of Nepal
were prepared by the Survey of India (SOI).
Subsequently, in 1950 by the US Army, in 1970 by
SoI and 1977 by the Government of Russia TBM of
Nepal were prepared. To address the need for technical
manpower and equipment for TBM preparation, the
Topographical Survey Unit was established in 1972
under SD, which was then upgraded to Topographical
Survey Branch in 1976. But it was not until 1993 when
Japan International Cooperation Agency (JICA)
aided in preparing 81 map sheets of the Lumbini zone,
that Nepal was actively involved in the topographic
mapping of the country (Wagle & Acharya, 2020).
This marks the beginning of the active involvement of
the Government of Nepal (GoN) for TBM preparation.
Right after this, Eastern Nepal Topographic mapping
(ENTMP) which produced (255 sheets of 1:25000 & 57
sheets of 1:50000 scale) & Western Nepal Topographic
Mapping (WNTMP) producing 254 sheets of 1:25000
and 79 sheets of 1:50000 map were carried out with
financial aid from Finnish International Development
Agency (FINNIDA). These JICA and FINNIDA map
series maps were subsequently digitized to produce a
Digital Topographic Database which is called NTDB
(Shrestha, 2009).
and producing updated maps. Initially, the rate of
the update was around 10 sheets per year (Wagle &
Acharya, 2020). Considering a total of 681 sheets
of the combined JICA & FINNIDA, at this rate, it
would have taken around 68 years to update TBM
of the whole Nepal, which would already have been
outdated. Thus, realizing the necessity to increase
the speed of updating, the SD since 2018 has been
updating more than 200 sheets a year using ZY-3
images provided by the Government of China. This
significant increase in target comes with many
challenges. During these two years, many challenges
have been faced and resolved and some are yet to
come. This paper presents the challenges faced during
different stages of TBM update and the way they were
handled. It also recommends some innovative ways
wherever applicable.
2.Current Status Of Topographic Map
From 2007 to 2017, in total around 70 map sheets
were updated. Since 2018, more than 400 sheets
have been updated, half of these map sheets are
ready for print validation and the remaining half are
currently undergoing cartographic work and will
Since 2004, the SD has been updating these databases shortly be ready for field verification. The speed
Figure 1: Topographic Map Sheets of Nepal from JICA and FINNIDA series.
Geomatics For Sustainable Development
of work has increased tremendously, but this has
increased difficulty in quality control. Due to the
large number of maps being updated, it is not possible
to check each map thoroughly. Thus, it is even more
important to consider every challenge that can arise
at every stage of map-making and prevent them
from happening rather than to check thoroughly
later and correct them. Making suitable strategies to
minimize the introduction of errors at different stages
from planning, image processing, georeferencing,
feature extraction, field verification, data collection,
symbolization, map layouts and printing is necessary
for wise utilization of available human resources.
A substantial time for fieldwork consisting of GCP
collection, feature extraction, field data collection
and field data verification followed by even longer
duration of data validation and cartographic work
was required in the first year to produce updated
NTDB and TBM, which was almost twice more than
initially planned duration. This, in turn, caused a
delay for work of the year that followed, but various
challenges faced in the first year were resolved before
moving to the field for the second year which helped
to some extent to make up for the delay. Section 3 of
this paper discusses these challenges, along with the
way they were handled.
3.Dividing Into The Challenges
This paper is all about the challenges which appeared
in every phase of update of TBMs. The methodology
followed for updating the TBM is shown in Figure
2. Various challenges were faced by the survey
professionals and management committee during this
procedure. The challenges in different phases are
discussed below.
3.1 Planning Phase
As with every project, success & smooth flow of
work of TBM updating depends upon the planning.
First of all, sites for sheets to be updated are selected
and different teams are assigned for different sheets
updating. In 2018, sheet division among teams was
such that different teams had to visit the same district
or even the same local unit for data collection & field
verification, which is not a very effective way. Sheet
division next year was planned so that any particular
team would have to visit certain districts and no two
Figure 2: Workflow diagram of Topographic map updating process.
teams would be visiting the same districts. Moreover,
in the previous year, teams were deployed for fieldwork
before proper planning for control surveying, which
resulted in wastage of resources for collecting
redundant ground control points. In the following
year with proper planning, it was easily avoided,
which saved a lot of time and effort. While planning,
it is important to study the accessibility, topography
and density of details at areas under targeted sheets.
With proper consideration, teams can be assigned
optimum routes and an equitable amount of work
thus avoiding wastage of resources & manpower. For
planning existing topographic databases, Images and
data from sources like google maps & OSM should
be studied.
Secondly, it is beneficial to complete the tasks that
can be completed in the office itself before moving
to the field. In the past just after image selection and
their processing, teams were deployed in the field for
data collection and verification. Thus, some members
were collecting Ground Control Points (GCPs) for
georeferencing, while others were collecting field
data from local units. As it is harder to distinguish
features like canal and road among others just by
looking at the image, later on, if data about them is
not collected in the field, then there arise chances for
blunder. To avoid that, an innovative approach would
be to complete feature extraction and digitization
field verification so that any possible
mistakes in identifying features can be checked and
corrected. It can be ensured by completing all tasks
of GCP collection, image processing, georeferencing,
digitization and feature extraction before moving to
the field for verification and data collection. Thus, a
change in methodology is required.
to reach at the exact location of features to be
collected and capture their location. Fortunately, there
are several official institutions which keep records of
various features that are to be shown in a topographic
map. Compilation of data from these sources before
moving to the field and their verification, later on,
would decrease the volume of work. Moreover, existing
topographic maps along with present satellite images
can be used to collect and verify attributes of features
easily identifiable in them such as road, buildings etc.
Applying this solution has to a great extent helped
gather more data, even when the location of those
features being collected is not accessible. Moreover,
collecting data after a long time requires a lot of
manpower and budget. If data is collected frequently
by compiling from different authentic institutions,
there won’t be much change so can be verified by
existing manpower with a minimum of expenses,
and can produce a map showing the current state of
the real world. Thus, by employing this innovative
approach of currency checking at frequent intervals,
it would be possible to circumvent large field works
demanding huge resources and many people.
3.3 Image Processing and Geo-referencing
TBMs are updated by using remotely sensed ZY-3
satellite images. Not all images would be equally
desirable for this purpose. Visually pleasing images
with minimum haze & cloud cover and preferably
of the same row or same path would make best
candidates. The extent of images dictates the
requirement of control points. If images can be
mosaicked or are at least overlapping properly this
would reduce the number of GCPs to be collected.
Now in the hilly region, collecting even a single GCP
can take up to 2 days, it would be beneficial to choose
images properly.
Finally, the inability to coordinate with concerned
local representatives and offices in the field area is
also a major challenge. A lack of prior information
to them had been a cause of delay in the past year
but can be solved by contacting and coordinating with The general process is, suitable selected images
are ortho-rectified & then pan-sharpened to obtain
them before moving to the field.
images with high spatial and spectral information.
3.2 Fieldwork Phase
Different pan sharpening techniques produce different
Fieldwork is a challenging task due to the difficult results. As of now, it has just been hit and trial.
terrain of most of the country and lack of good Proper testing of different techniques with different
accessibility. For these reasons, it’s almost impossible images and coming up with recommendations would
Geomatics For Sustainable Development
be helpful, as pan-sharpening takes quite a bit of
time. After pan-sharpened images are obtained,
these are to be georeferenced so that existing topo
data can be overlayed with them to identify and
update the changes. The main problem here lies in
the transformation parameters. With GNSS survey,
GCP coordinates are obtained in WGS 1984 ellipsoid
whereas existing topo data have a coordinate system
based on Everest 1830 ellipsoid. The uncertainty of
exact parameters for transformation between these
two coordinate systems contributes to a large shift in
the existing database and image to be overlayed. Using
different sets of parameters resulted in a shift of up to
22m. To avoid this shift, transformation parameters
for FINNIDA series were tested on multiple images
and their shift with the existing database was almost
found to be under the permissible region. Thus, using
these parameters, WGS 84 and Everest 1830 based
coordinate systems can be easily transformed between
one another, which has helped to compare with data
from different available sources.
Besides these, a major challenge that arose in the past,
due to lack of coordination between different groups
while georeferencing, is difficulty in edge matching.
Images were not exactly seamless and there were
visible shifts in data of adjoining groups in the margin.
In the later year, this challenge was solved by using
the same georeferenced images by multiple groups
wherever possible. This has led to creating seamless
data more easily.
Figure 3 Shift in images of two groups at edges.
3.4 Feature Extraction and Digitization
After overlaying an existing database with
georeferenced images, updating is done by digitization
which is highly labour intensive. Simply digitizing
may not require highly skilled manpower, but one
without knowledge of different relationships that exists
between different data such as contour & streams,
road and contour, etc. may not produce correct data.
Also, there lies some subtle differences with features
from different topography. Prior knowledge of what
kinds of features exist in the region and what they
look like along with the ability to understand existing
databases is essential to ensure the correctness of
First of all, in this stage, major problems arose from
wrong estimates of the capacity of manpower due
to the inability to correctly recognize the difference
between nature and volume of details in the past &
present year. For example, Roads in terai are straight
and visible so can be easily digitized accurately
without zooming much. However, for hilly regions,
these have many bends, and one should consider not
only accuracy but also a cartographic generalization.
Thinking that people gained experience by updating
maps in Terai, they were without any further training
assigned to update maps of the hilly region. This
resulted in digitized roads with sharp bends and
overlapping features when printing or at reference
scale. Thus, thinking beforehand about possible
differences in work, manpower must be trained for
such cases, so that repetition of work and wastage of
resources can be prevented. Moreover, features are
digitized sometimes with incorrect attributes. This
incorrect attribute is partially due to inconsistency
in feature code representing attributes. A lack of
complete symbology and list of feature codes has
caused us to create new symbols & define new feature
codes as we go, and has sometimes caused conflict.
As these codes and symbols are changed many times
before finalizing there lies the chance of these codes
not -being updated properly in some data. Thus,
studying possible features that will be encountered and
then defining symbols and feature codes beforehand
could mitigate this challenge. As of now, almost all
of the features that have been encountered has been
given proper feature code and symbology, making an
exhaustive list is surely necessary for consistency of
work. Compiling data from authentic sources and
modifying them would minimize incorrect attributes
and even reduce the number of new features to be
digitized from scratch. Proper training to avoid
topological errors should be given so that time can be
saved frequently checking and correcting topological
errors. A less labour-intensive approach should be
applied wherever possible. For example, the available
image can be classified to produce land cover data.
Developing a suitable model to produce land cover
would save the labour needed for digitization.
Secondly, the lack of powerful computers and software
is also a big problem. Sometimes programs crash
midway while digitizing, causing loss of progress.
Identifying and distinguishing features also becomes
cumbersome looking on these laptops. Computers
become slower with use and hinder the speed of
digitization. Moreover, laptops with a small screen are
not ideal for digitization. Thus, a simple solution lies
in providing powerful desktops with large monitors
and genuine software to help digitize faster and more
3.5 Map compilation
This is the stage that has seen most innovation and
has had a great amount of reduction in complexity.
During map compilation, all data are presented in
a predefined layout. Map title sheets no., legends
and other marginal information are added. Grids,
graticules and their values are added, features are
labelled and those labels are placed at appropriate
positions. Just a year back, all these tasks were very
labour demanding but now they have become much
easier. Labels of features can be easily managed
as annotations. Grid and graticules, as well as
sheet no. and titles, can be automatically generated
reducing chances of human error & requirement of
human labour. Templates are ready to use and can
be changed easily as most of the map elements have
been created now as features in a database, thus can
be easily added to as many map documents and as
many different templates as needed. Thus, finalizing
the database is almost finalizing the map. Moreover,
symbology for almost all encountered features is
also prepared. After map compilation, comes map
printing and reproduction, where the challenge was
of colour management. However, by using CMYK
Figure 4: Some problems in digitization: (a) sharp bends (b) undigitized roads (c) wrongly digitized roads
(d) different land cover categories at the edge (e) intertwined road and hydro lines (f) discontinuous road
(g) intertwined old trails and new roads
Geomatics For Sustainable Development
colour charts to pick appropriate colour values for
symbols in the map, exporting the map in the same
colour system and printing with the same colour
system has solved that. Now, these maps, which after
all these stages, test-printing & validation can be
mass-produced as required using a computer to plate
technology in offset printing.
Government of Canada, 2011. National
Topographic System. Retrieved January 22,
2020, from https://www.nrcan.gc.ca/earthsciences/geography/topographic-information/
Cartography: Visualization of Spatial Data,
1st ed.; Pearson Education Limited: Essex,
UK; pp. 205.
Shrestha, K. G., 2009. Updating of topographic
maps in Nepal. Geoinformatics Journal of
Nepal, vol.VIII, pp. 52–56.
Wagle, N., & Acharya, T. D., 2020. Past
and Present Practices of Topographic Base
Map Database Update in Nepal. ISPRS
International Journal of Geo-Information.
9(6), pp. 397, doi:https://doi.org/10.3390/
4.Discussions And Conclusions
Used for navigation, planning & implementing
development projects, topographic maps need to be
up-to-date to reflect the correct state of the real world
and help make appropriate plans. Realizing this, the
SD has prioritized this task, and the TBM update has
gained huge speed these past two years. However,
several challenges lie ahead. Maps in the Terai
region have been updated, and now these in hilly
and mountainous regions are to be updated. These
areas present more challenges in terms of terrain,
accessibility, ability to coordinate with concerned
local offices and the sheer
amount of digital work to be done. Mapping these
regions may require new methodology, symbologies,
map layout and training of manpower. Many
challenges are being resolved as we’re learning
from experience, but that seems not to be enough.
So, learning by studying what we may encounter
has also been equally important. Proper planning,
coordination with concerned authorities, training
manpower, proper assignment of areas to teams,
making available required machines and software,
employing automatic feature extraction, compilation
of data from available sources would help in reducing
the difficulty of tasks and solve most of the challenges.
Checking the currency of maps at frequent intervals
will help to produce high quality up-to-date
topographic maps with minimum human labour
and expense of resources in the future. A developing
country like ours should make a go for these.
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