ICETACS 2013

978-1-4673-5250-5/13/$31.00 ©2013 IEEE

Management and Validation of VGI

Vartika Bajpai

GIS Cell

MNNIT

Allahabad, India

D.K. Yadav

CSED

MNNIT

Allahabad, India

Abstract-With the advent of web based geospatial

applications or geo-portals which allow for access and

exchange of geographic information through the internet, the concept that enables users or individuals to contribute

geographic content and other information related to it, has

become a new area of research in Geographic Information

System(GIS). Enabling users to add information promotes

city development because local people have better knowledge about the area. Though volunteered geographic information

(VGI) offers numerous advantages but it also has many

challenges associated with it. The foremost challenge is

authenticity and validation of user added information. In this

paper, a design is devised and implemented using open source web GIS tools like Geoserver, OpenLayers and Postgis, for

management and validation of geographic content generated

voluntarily.

Keywords- open source GIS; VGI; Web GIS; Volunteered

GIS;

I. INTRODUCTION

Earlier it was believed that map making and data

creation was the role of cartographers, surveyors and

professional experts in this area. The data created by these

cartographers and experts is used in planning. With the

advent of web 2.0 the focus has been shifted from regional

level planning to local level planning. As per the changed

focus, the data available is in abundance but not up to the

mark or as required for local level planning. When we talk

about data collection at micro-level, data collection using

traditional GIS techniques is costly and time consuming,

that necessitates the need of Volunteered Geographic

Information (VGI)

VGI provides an innovative and more flexible mode to

gather information, besides the traditional modes of data

collection. With the advent of Internet associated with Geo

Web 2.0 and smart mobile devices embedded with Global

Positional System (GPS) receivers, now the users can help

in acquiring data, which was difficult to collect and

manage earlier. This mode of data collection is called VGI

[1]. Volunteered Geographic Information which is

contributed by public can be added through two means:

Web based platform that allows creation of point, line and polygon feature manually using some

input pointing device like mouse etc.

GPS receivers embedded in handheld GPS and smart mobile devices.

Using GPS units embedded in mobile devices can be a

better way than using handheld GPS for 2 reasons:

Ease of availability of mobile devices. As we are

talking of data generation by public, therefore smart mobile devices (in trend) are easily available with

local people than the handheld GPS devices .

Attribute information related to target feature or

point of interest (POI). Handheld GPS receivers can only provide latitude and longitude co-ordinates,

whereas VGI applications based on mobile along with recording location coordinates can also provide

details like name, description etc about the POI.

In this paper, a design is devised and implemented for

management and validation of geographic content created

by user either using web interface or mobile interface. The

implementation of web interface for data collection and

validation of that data is carried out using open source web

GIS tools like Geoserver, OpenLayers and Postgis. The

implementation of mobile application for geodata

collection is done using android application programming

interface (API). The rest of the paper is organized as

follows. Section 2 describes the related work. Section 3

describes our approach for the management and validation

of user created geographic data. Section 4 describes the

implementation of the approach and the results (screen

shots). And finally Section 5 is the conclusion.

II. RELATED WORK

The concept of user generated content was proposed by

Goodchild [1].User generated geographic content has

numerous terms associated with it such as: VGI,

crowdsourcing etc, where “citizens voluntarily collect,

organize and/or disseminate geographic information and

data in such a manner that the information can be used by

many others” [2].

The advent of internet GIS and smart mobile devices

have enabled the usage of VGI in many applications:

disaster management for reporting violent acts during

crisis (http://www.ushahidi.com/), transportation for

reporting traffic congestion related problems, urban

management for reporting informal settlements and illegal

developments in the city [3]. VGI is user generated content

therefore validation of data is essential so that the

information can be utilized fruitfully. Xialin Qian et.al [4]

have described about the type of validations required for

geographic content generated by user. Peter Mooney et.al

[5] have discussed how citizens have turned from

consumers of spatial data to generators of spatial data.

They have described about the inconsistencies associated

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with the user generated data with specific emphasis on

OpenStreetMap. But the literature mentioned above, either

describes the importance of VGI in different domains or

discuss about the credibility issues related to it but none of

them describes about the implementation of framework

that could control the management and validation of VGI.

Therefore it necessitates a need of framework that can

control, manage and validate the user generated

geographic content through both ways (mobile and web

interface). In this paper a design is devised and

implemented for management and validation of geographic

data generated by user either through mobile or web.

III. FRAMEWORK FOR MANAGEMENT AND VALIDATION

OF VGI

The architecture of this web based system is based on

the 3 tier client server model (Fig.1), which has 3 parts:

Web Browser, Map Server and Database Server. Based on

this web GIS architecture, the web based s ystem

developed consists of 3 parts (Fig. 2): Layer Panel, Map

Panel and Tool Panel. Layer Panel consists of several

layers for e.g. roads, railways, ATMs, bus-stops etc. Layer

Panel consists of 2 parts: Existing Layers and Public Data

Layers. Existing Layers contains data from trusted source

or after administrator’s approval(in case of user generated

data).Whereas Public Data Layers contains data created by

user(before administrator approval).Map panel is for

displaying the base layers and other overlaid layers by

select of layers in layer panel. Tool Panel consists of the

web based editor part which allows user to add geographic

content. The architecture for mobile application developed

for collection of geographic content is shown in Fig. 3.

Figure.1 Web GIS Architecture

Figure 2 The Web Based System

Figure 3 Architecture of the Mobile Application

A. Role based approach

In VGI applications, all the information or content

provided is provided by the users, therefore there is always

a question on the credibility of the user provided content.

Here comes a serious issue called Trust. Therefore a role

based approach is required where users can be grouped in

3 categories General users, registered users and

administrator. The general users can view, query and

perform analysis on the spatial data. Registered users apart

from having all these privileges can also add point, line or

polygon features and attribute information related to it.

Users can add content to the existing layers and can add an

unclassified feature. Unclassified feature here means that

user is not restricted to add information only in existing

categories (or layers) but can add any kind of geographic

information. User added information will not alter the

original database schema. A public schema has been

created with 3 tables namely point_type, line_type,

polygon_type. The user added content will be initially

inserted in any one of table depending on the geometry of

Layer Panel

Map Panel

Tool Panel

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content. Now here comes the role of the administrator.

Administrator will be the one, who will be fully aware of

the local area. Administrator will approve or delete the

user added content based on his knowledge.

Figure 4 Role Based Approach

Figure 5 Database Structure

B. Data Validation Approaches

Data Validation is required to detect and remove the

errors in data which makes the data accurate. The 3 main

types of Data validation for geographic information are:

Attribute Value Validation.

Duplicate Geometry Check and Topological Conflicts Check.

. In the following section, we present how we have dealt

with these validations

1) Validation of Attribute Values:

Attribute information related to POI is equally important

as the geographic content, because it helps in identifying

that specific feature among all other features in the map.

Geographic information can be extracted from

traditional GIS data collection methods like satellite

imageries etc but obtaining attribute information can be

costly and time consuming using these methods. This

information can only be provided by the public, like name

of the building, number of floors in building ,population in

that building etc.

Validation of attribute values involves checking the

attribute values against certain constraints like NOT

NULL constraints, domain constraints, maximum and

minimum length constraints etc. They are known as

integrity constraints in RDBMS. The implementation of

the web based system checks all these constraints, which

do not allow the user to enter semantically incorrect

attribute values.

2) Duplicate Geometry Check and Topological

Conflicts:

Duplicate geometry check means detecting those

geometries which are very near to each other. Whereas

topological conflicts means for example there cannot be a

building in the middle of the road.

As per our database design, the user created information

initially (before administrator approval) is added in any

one of its corresponding 3 tables (point/line/polygon),

depending upon geometry, in public schema.

Administrator can view all this information on the map

under public data layers. Therefore the process of

identification of duplicate geometries and topological

conflicts is based on the administrator’s knowledge and his

visualization. The identified feature violating any of the

constraint can always be deleted by administrator.

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Figure 6 Application Architecture

IV. IMPLEMENTATION OVERVIEW

There are many questions about the management of VGI

data. We have proposed a design which allows addition of

VGI data along with proper validations, which makes the

management of the VGI data easy. For adding new feature,

overall procedure (including validation) will be: first

registered user will draw(web based editor)/record(mobile

based) the feature of his choice (Fig.7&8), while entering

the attribute information, the attribute value constraint will

be checked (In Fig.8, the length value entered by user is

character and required value is numeric,hence it shows an

error message), and after successful verification of

attribute value constraint, user data will be added in any

one of the 3 tables under public data layers

(point/line/polygon) in public schema, original database

tables will not be altered without administrator approval.

Once the administrator performs Duplicate geometry

check and topological constraint check (Fig. 9), and no

user added geometry voliates these constraints,then that

user added feature will be approved and will be populated

as layer in layer panel of web based application.

Figure 7 Mobile Application for Feature Recording

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Figure 8 Attribute Value Validat ion when user entered incorrect value for length field

V. CONCLUSION

The development of the web based system for

management and validation of VGI supports the idea of

smarter cities. Web based VGI systems, developed using

open source GIS tools, being cost effective and time

saving, are becoming an alternative for data collection.

Data creation by user, using web based editor or mobile

based GIS application, is a viable way. In fact, Users using

mobile based GIS application for geographic data

collection is a better way because it provides a better

accuracy. The application (web based editor and mobile

application) designed and developed is tested with IITB

campus data. The application developed here is used for

local area management as local people have better

knowledge of the area. The entire package (data capturing

and data validation process) can serve as an efficient

means for R&D organizations willing to build geospatial

application seeking for public contribution in geographical

data creation. However, while designing an interface for

rendering the map along with proper layer selection

options (using OpenLayers) on the mobile screen would

require some amount of adjustment. In our approach of

validation, the topological check and duplicate geometry

check is based on the visualization of data by the

administrator. This web based system developed could be

improved, for better accuracy, by using spatial clustering

algorithms such as k-means algorithm (for Duplicate

geometry check).

ACKNOWLEDGMENT

We would like to thank Prof. N.L. Sarda, Department of

Computer Science and Engineering, IIT Bombay, Dr.

Smita Sen Gupta, Research Scientist, GISE Advance

Research Lab, IIT Bombay for their valuable guidance and

support.

Figure 9 Administrator Logged in: admin will delete or approve the feature by visualizing it on the map

REFERENCES

[1] M.F. Goodchild, “Citizens as Voluntary Sensors: Spatial Data Infrastructure in the World of Web 2.0,” International Journal of Spatial Data Infrastructure Research, 2007, Vol.2, pp.24-32.

[2] David L.Tulloch, “Is VGI participation? From vernal pools to video games,” Geojournal, 2008, Vol 72, pp.161-171

[3] Song Weidong and Sun Guibo, “The role of mobile volunteered geographic information in urban management,”18th International Conference on Geoinformatics, 2010, pp.1-5.

[4] X.Qian, L.Di, D.Li, P.Li,L .Shi and L.Cai , “Data Cleaning approaches in Web 2.0 VGI application,”17th International Conference on Geoinformatics,2009, pp.1-4

[5] Peter Mooney, Padraig Corcoran, Huabo Sun, Lei Yan, “Citizen generated spatial data and information: risks and opportunities,” International Conference on Industrial Control and Electronics Engineering, 2012, pp.1990-1993.

[6] Sarah Elwood, “Volunteered geographic information: future research directions motivated by critical, participatory, and feminist GIS,” Geojournal, 2008, Vol. 72, pp.173-183.

[7] Lijing Zhang, Jing Yi, “Management Methods of Spatial Data Based on PostGIS,” Second Pacific-Asia Conference on Circuits, Communication and System (PACCS), 2010, Vol.1, pp. 410-413.

[8] Song Weidong and Sun Guibo, “Using Mobile GIS as Volunteered GI provider,” First International Conference on Information Science and Engineering (ICISE), 2009, pp.2229-2232.