Southeast Asian Studies, Vol. 46, No. 4, March 2009

3D Topographical Analysis of Hanoi, Vietnam

YONEZAWA Go*

Abstract
Analyzing the relief of terrain and the micro-topography of Hanoi can play an important role inexplaining its urban transformation. To analyze topographical changes, it is necessary to use
elevation data to generate a digital elevation model (DEM), a digital representation of groundsurface and the most important element of topographical analysis for urban transformation,
providing evidence for the existence of features such as old rivers, lakes, ﬁlls and land subsidence.
Consequently, the DEM of Hanoi in 2005 was generated with data collected for 8,015 points.
Based on the surface estimation method using Cubic B-Spline Function, the DEM is generated at
2-meter resolution. The contour interval is 0.5 meter. The very subtle elevation gaps which
can not be distinguished on the satellite image are signiﬁcantly recognizable on this DEM. A
second DEM was generated from the topographical map prepared by the French government in
1950, now held in the French library. This DEM at 2-meter resolution is also based on DEM
generation using the method of STRIPE. By comparing the two patterns of DEM for 1950 and
2005, the areas of ﬁlls and land subsidence can be clariﬁed.
Keywords : Hanoi, urban transformation, topographical map, dike, DEM, GIS

Introduction
Hanoi, the capital of Vietnam, is one of the fastest-growing cities in Southeast Asia.

Before the19th century, the city contained many lakes and ponds which were relict lakes of Red River.
th

the early 20

century, however they disappeared almost completely from the map.

outline of this urban transition is explained by Sakurai and Shibayama [2007].

In
The

Practically, it isveriﬁed by Yonezawa and Shibayama [2007] and Duan and Shibayama [2008] using GIS(Geographic Information System) and remote sensing technology.
Two key points have inﬂuenced urban transformation in Hanoi.
under French rule in the late 19th century.

One is that Vietnam was

Urban planning by the French government had aprofound inﬂuence on the urban development of Hanoi.

The second is the geography of Hanoi

and its natural environment.

Hanoi is located in a ﬂoodplain of Red River, the average elevation

being less than 10 meters.

It has faced repeated ﬂooding for a long time.

According to themap drawn by the French government, there was already a large-scale dike in the late 19th
* 米澤

剛，Institute of Sustainability Science, Kyoto University
e-mail: go-yone@cseas.kyoto-u.ac.jp519

東南アジア研究46巻 4 号

century.

This is one of the most important points to consider the topographical changes in

Hanoi.

However, it is difﬁcult to describe the topographical changes using two-dimensional(2D) analyses only.
Yonezawa [2008] suggested a three-dimensional (3D) urban model consisting of threeelements: aboveground data, topographical data, and subsurface data.
expected to be the basis data of various area studies.

Such a model can be

The present study focuses on the

topographical changes of Hanoi in the 19th and 20th centuries.

To analyze the relief of terrain

and micro-topography for such an urban transformation, we need to use elevation survey datato generate a digital elevation model (DEM), a digital representation of ground surface and themost important element of topographical analysis for urban transformation, providing evidence
for old rivers, lakes, ﬁlls and land subsidence.
(2005 and 1950) were generated.
can be visualized.

Consequently, two patterns of DEM of Hanoi

By comparing them, the areas of ﬁlls and lands subsidenceThis will be useful for studying urban transformation, because it is difﬁcult

to estimate how many lakes and ponds disappeared by using only 2D spatial analysis.

Urban Transformation of Hanoi
Fig. 1 shows the urban transition of Hanoi.
many lakes and ponds all over the city.

Fig. 1 (a) is a historical map of 1873, which shows

According to Haruyama [2004], the construction of adike in Hanoi is the biggest reason for their presence.

東南ア4604-3,1a

Hanoi is located in a ﬂoodplain of the

東南ア4604-3,1b(a) Historical map of 1873(b) Satellite (IKONOS) image of 2005

Fig. 1 Urban Transition of Hanoi
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YONEZAWA G. : 3D Topographical Analysis of Hanoi, Vietnam

Red River, the average elevation being less than 10 meters.
from ancient times.
city.

Many ﬂoods have struck Hanoi

Therefore, the construction of a dike was necessary to protect the capital

When the mainstream of the Red River was cut by construction of the dike, some of themeander channels were left as oxbow lakes and channels in the ﬂoodplain.
Kiem Lake are typical examples.
higher each time.

Tay Lake and Hoan

Although the dike was broken several times, it was rebuilt

Thus, infrastructure construction for ﬂood-control can be found much earlier

in Hanoi.
Fig. 1 (b) is a satellite (IKONOS) image of 2005.
have disappeared.

The lakes and ponds that existed in 1873

Thus, the apparent changes in the past 130 years are shown visually.

Sakurai and Shibayama [2007] showed from historical materials (i.e., old maps and literature)that obvious urban transformation of Hanoi occurred during the Nguyen Dynasty period(1802-1945).

This change would be related to French government planning.

BecauseVietnam was under French rule from 1887 to 1954, French army headquarters werestrategically placed in the Thang Long Citadel (central Hanoi).
military facilities in the citadel.
1930s.

At ﬁrst, the French built many

Urban development centered on the citadel continued until theIt was developed by the continuous land-ﬁlling of many lakes and ponds.

This wasveriﬁed by Yonezawa and Shibayama [2007] and Duan and Shibayama [2008], suggesting
different approach to history or area studies using the methods of information technology andinformatics such as GIS and remote sensing.

However, it is difﬁcult to understand two-

dimensionally the problems of how lakes and ponds were ﬁlled and how the construction of thedike inﬂuenced the urban environment of Hanoi.

It is necessary to analyze geomorphic change

three-dimensionally to answer these questions.

Consequently, using DEM can be an effectivemeans to analyze urban transformation.

Generation of High Resolution DEM
There are no high resolution DEM in Vietnam like “Digital Map 50 m Grid (Elevation)”published by Geographical Survey Institute in Japan.
resolution DEM based on various data.

Therefore, we need to generate the highIn this study, the DEM of Hanoi is generated from

SRTM, survey data and a topographical map.
Utilization of SRTM
The digital elevation data of SRTM (Shuttle Radar Topography Mission) is one of the most
famous DEMs, covering the entire world.

The SRTM is an international project produced by

the National Geospatial-Intelligence Agency (NGA) and the National Aeronautics and Space
Administration (NASA).

The SRTM data has two patterns of resolution, the resolution of

SRTM-3 is about 90 m, and that of SRTM-30 is about 900 m.
covers all land area of the earth.

SRTM-3 is the only DEM which

Thus SRTM-3 is useful for natural environment analysis anddevelopment project work in areas where DEMs cannot easily be prepared.
SRTM-3 data for the area that contains Hanoi is shown in Fig. 2 (a).

It is a mosaic image521

東南アジア研究東南ア4604-3,2a

46巻 4 号

東南ア4604-3,2b(a) Elevation data of areas surrounding Hanoi from
SRTM-3(b) Elevation data in Hanoi from SRTM-3

Fig. 2 Visualization of SRTM-3 Data (from NASA)

that connects four data (N20E105.hgt, N20E106.hgt, N21E105.hgt, N21E106.hgt) together.
These data can be downloaded from NASA web page.1) The bottom-left corner of thedownloaded ﬁle “N20E105.hgt” means latitude 20°N and longitude 105°E of WGS 84 as ageographic coordinate system.

Fig. 2 (b) is the central area of Hanoi.

detailed changes in such a ﬂat terrain.

However, we cannot see

Because the resolution is too low for analyzing theurban transformation of Hanoi, it is necessary to generate a much higher resolution DEM.
Utilization of Survey Data
Fig. 3 (a) shows a result map (paper map) of an elevation survey.

The scale is 1: 2,000.

Twenty-one such maps were collected through Hanoi University of Mining and Geology.
example of survey data is listed in Fig. 3 (b).

An

The numbers next to the encircled points areelevation data (meter).

Fig. 3 (c) shows the whole area of the elevation survey, being acomposite of the 21 maps.

The survey area is 5 km×5 km, and the number of survey points is

8,015 (Fig. 3 (d)).

First, a DEM was generated for the area of the old quarter (Pho Co district).

The DEM was generated as follows:(1) Input the point data (x, y, z)First shows the paper map including the survey data was converted to digital data by scanning.
Fig. 4 (a) shows the survey data on the map.

The coordinates (x, y, z) of each point can be readby using painting software (Adobe Photoshop, Corel Paint Shop Pro and so on).
position and z is its elevation (meter).

This can be converted to latitude and longitude by an

1) SRTM; http://www2.jpl.nasa.gov/srtm/
SRTM Data; ftp://e0srp01u.ecs.nasa.gov/srtm/
522(x, y) is a pixel

YONEZAWA G. : 3D Topographical Analysis of Hanoi, Vietnam

東南ア4604-3,3a

東南ア4604-3,1b(a) Result map of elevation survey(Scale 1 : 2,000)(b) Example of elevation data. Numbers next toencircled points are elevations (meter)

東南ア4604-3,3c

東南ア4604-3,3d(c) Area of elevation survey (Composite of 21maps)(d) Visualization of survey points (8,015 points)

Fig. 3 Elevation Survey Data of Hanoi

afﬁne coordinate transformation.
(2) Estimate the topographical surface using the developed program
The topographical surface is estimated from (x, y, z) based on the surface estimation method (wecall it BS-Horizon) using the Cubic B-Spline Function [Nonogaki et al. 2008].

BS-Horizon is oneof the surface estimation programs for geologic boundary surfaces and geomorphic surfaces.
The data of Step 1 is input into this program.
(3) Output the topographical surface (DEM)523

東南アジア研究46巻 4 号

東南ア4604-3,4a

東南ア4604-3,4b(a) Survey points of old quarter (Pho Co
district)(b) Example of generated DEM with contours at
intervals of 0.5 m

東南ア4604-3,4c(c) Map (1 : 2,000) overlaid with generated DEM
Fig. 4 DEM Generation of Old Quarter (Pho Co district)

The generated DEM of the old quarter of Hanoi is shown in Fig. 4 (b).
meters and the contour interval is 0.5 meters.
in the generated DEM.

The resolution is 2

Hoan Kiem Lake and the Great Dike are visible

The highlighted area has a high elevation.

Fig. 4 (c) is an example of

the generated DEM overlaid on the original map (1 : 2,000).
Fig. 5 (a) shows a DEM of the survey area (5 km×5 km), which is deﬁned as the 2005 DEM.
It includes 8,015 points of survey data.
524

All point data are shown in Fig. 3 (d).

Fig. 5 (b) is a

YONEZAWA G. : 3D Topographical Analysis of Hanoi, Vietnam(b)
東南ア4604-3,5a

東南ア4604-3,5b(a) Visualization of generated DEM(b) Visualization of generated DEM with
contours at intervals of 0.5 m

Fig. 5 DEM Generation of Hanoi

contour map with a contour interval of 0.5 meters.

The very subtle elevation gaps which can

not be distinguished on SRTM data or the satellite image are signiﬁcantly recognizable on it.
An example of the visualization of 3-D DEM is shown in Fig. 6 (a) using the NVIZ
visualization tool in GRASS GIS software.2) Fig. 6 (b) shows the generated DEM overlaid on
the original map (1 : 2,000).
Utilization of Topographical Maps
The topographical map used was generated by the French government in 1950 and comes fromthe French National Library (Bibliothèque nationale de France) as paper map (Fig. 7 (a)) with ascale of 1 : 4,000.

Fig. 7 (b) is an example of contours at intervals of 0.5 meters.

The DEM at 2m resolution is generated based on the STRIPE method (Fig. 8) [Noumi 2003]. The STRIPE
method is an efﬁcient means to generate a DEM from a topographic map.

The elevation f (xp,yp) at a point (xp, yp) in a space between two successive contour lines h and H must be
h＜(xp, yp)＜H.
Based on this idea, we can quickly generate a DEM by assigning the inequality constraints
to each point in a space between contour lines after scanning a topographic map.
shown in Fig. 9 (a), which is deﬁned as the 1950 DEM.

This result is

The contour interval is 0.5 meters.

2) GRASS (Geographic Resources Analysis Support System) is a software for performing spatial analysis.
It consists of more than 350 modules for processing vector (2D/3D), raster and voxel data. Manyinterfaces to other programs in related domains like geostatistics, databases, mapserver and even other
GIS software exist. Nviz is a visualization tool of GRASS. It is used for dynamic visualization ofgeologic cross-sections and generation of animated image sequences. URL; http://wgrass.media.osakacu.ac.jp/grassh/525

東南アジア研究46巻 4 号

東南ア4604-3,6a(a)(a) 3D visualization of generated DEM of Hanoi

東南ア4604-3,1b(b) 3D visualization of map overlaid with generated DEM
Fig. 6 Example of 3D Visualization

Fig. 9 (b) shows the generated DEM overlaid the topographical map (1 : 4,000).

Fig. 9 (c) shows

the accuracy of STRIPE method, which closely reproduces the original contours.
Unfortunately, the only topographical maps available were the survey data in 2005 and theFrench topographical map of 1950. However, comparison of the two DEMs can be expected toshow the urban transformation of Hanoi from a topographical perspective.

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YONEZAWA G. : 3D Topographical Analysis of Hanoi, Vietnam

東南ア4604-3,7a(a)(a)

東南ア4604-3,7b

Topographical map fromgovernment (Scale 1 : 4,000)

French(b) Example of contours at intervals of 0.5 m

Fig. 7 Topographical Map of 1950

東南ア4604-3,8Fig. 8 Generation of DEM Using the STRIPE Method527

東南アジア研究46巻 4 号

東南ア4604-3,9a

東南ア4604-3,9b(a) Visualization of generated DEM with contours at
intervals of 0.5 m(b) Map (1 : 4,000) overlaid with generated
DEM

東南ア4604-3,9c(c) Accuracy of STRIPE method
Fig. 9 Generation of DEM from Topographical Map

DEM Analysis
The DEM of Hanoi was generated using the random survey data of 8,015 points in the city.
The survey data can be sorted into data on roads and data on the topographical surface.
528

This

YONEZAWA G. : 3D Topographical Analysis of Hanoi, Vietnam

東南ア4604-3,10a

東南ア4604-3,10b(a) Visualization of survey points on roads(2,748 points)(b) Visualization of DEM generated using survey
data on roads

Fig. 10

Generation of DEM Using Survey Data on Roads

東南ア4604-3,11a

東南ア4604-3,11b(a) Visualization of survey points on the
topographical surface (5,267 points)(b) Visualization of DEM generated using survey
data on the topographical surface

Fig. 11

Generation of DEM Using Survey Data on the Topographical Surface

enables two kinds of DEM to be generated.
the roads is shown in Fig. 10 (a).

The distribution of the elevation data of survey on

The number of data points is 2,748.

Fig. 10 (b) is an exampleof visualization of the DEM generated using the survey data on roads.

The roads and the dikeon this DEM are clearer than on the DEM generated from all survey points.

The distributionof the elevation data of the survey on the topographical surface is shown in Fig. 11 (a).
number of data points is 5,267.

The

Fig. 11 (b) is an example of visualization of the DEM generated529

東南アジア研究46巻 4 号

東南ア4604-3,12a

東南ア4604-3,12b(a) Result map of difference between 2005 DEM and1950 DEM
Note: The darker-shaded area is higher in 2005 than
1950.

(b)

Fig. 12Map (1 : 2,000) overlaid withdifference of DEM
Note: The darker-shaded area is lower
in 2005 than 1950.

Difference of DEM (2005 and 1950)

using the survey data on topographical surface.

The detail of the topographical surface can beobserved in this DEM.
The difference between the 2005 DEM and the 1950 DEM is shown in the result map in
Fig. 12 (a).

The darker-shaded area is higher in 2005 than 1950. Two remarkable points

emerge from Fig. 12 (a).
2005 than 1950.

One is that the elevation of the Great Dike is about 2 meters higher in

The average height of the dike in 2005 is about 12 meters, compared with

about 10 meters in 1950.

This difference shows that the dike has been raised since 1950.

Haruyama [2004] showed the height of the dike in 1809 was 3.5 meters from several historicalmaterials.

Therefore, the height of dike has been increasing with the passage of time.

The second point that emerges from Fig. 12 (a) is land subsidence in Pho Co district.
12 (b) shows the 2005 map overlaid with the difference map of Fig. 12 (a).
areas have lower elevation than in 1950.

Fig.

The darker-shaded

The average elevation of Pho Co district is about 9

meters in 2005, which is 0.5 meters lower than the elevation in 1950.

Therefore, land

subsidence has occurred.

Conclusion
In this study, the DEM of Hanoi in Vietnam was generated from the elevation survey data and a
topographic map.

The very subtle elevation gaps which cannot be distinguished on thesatellite images are signiﬁcantly recognizable on the DEM.

These high resolution DEMs areuseful not only for analyzing the urban transformation of Hanoi, but also for the urban
sustainability of Hanoi, as in improvement of urban infrastructure and disaster prevention.
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YONEZAWA G. : 3D Topographical Analysis of Hanoi, Vietnam

The generated DEMs give us not only detailed information about the terrain of Hanoi, butalso information on landform changes over approximately 50 years.

There are two notablechanges: (1) construction to raise the dike, (2) the change of terrain around Pho Co district.

In

future, the relation between ﬂooding and the construction of dikes would be the most importantelement to study in this area.

Hanoi will celebrate its 1,000th anniversary in 2010.

Throughdikes this city has been protected from flooding by the Red River for a long time.

It isnecessary to consider the effects of dikes on the urbanization and the life of residents.
Additionally, it is necessary to search for traces of ancient rivers and landﬁlls from thegenerated DEM.

These signs can be more practical indicators when we consider the relation

between urban transformation and topographical changes.
Acknowledgement
This research is based on “Development of system for spatiotemporal mapping with emphasis on urban
area in Southeast Asia” supported by a Grant-in-Aid for Young Scientists (B) (Issue No. 19710208, Go
Yonezawa, Kyoto University); “Development of Area Informatics: With Emphasis on Southeast Asia” in
Scientiﬁc Research (S) (Issue No. 17101008, Mamoru Shibayama, Kyoto University); and “Impacts ofDevelopment Programs on Sustainable Use of Ecological Resources of Southeast Asia” (Yasuyuki Kono,
Kyoto University) in the Integrated Research of Institute of Sustainability Science, Kyoto University.
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