Internet Mapping: Data Management & Transfer Technology

Shibu VargheseDaniel TurnerRussell Frith

Introduction

• Web GIS: GIS over the web!• Webmap presentation consists of “public visual thinking” and

“private visual thinking.” Two distinct areas for evaluation. Read authors’ paper for more details!

• Literature search reveals volumes of expertise in design considerations for Internet mapping

• Compare vendors’ implementations using a benchmarking technique.

• Vendors Compared:

Benchmarking Specification

• Topics1. Geospatial Data I/O2. Communicating Geospatial Data to the Public

3. Webmap Application for “Private Visual Thinking”• Each topic consists of one or more tasks

for the evaluation• Each topic is accompanied by

observations.

Handling Geospatial Data

• File Formats– Web GIS must have functionality to handle standard GIS file

formats– Web GIS software must be able to handle both vector data and

raster data (i.e. TIFF)• Databases

– Web GIS software must be able to handle thematic data by accessing ODBC drivers

• Map Projection, Coordinate System, and Unit of Measurement– Web GIS software must be able to define map projection,

coordinate system, and unit of measurement

ArcView Shape

TIFF

ODBC

Coordinate System Miles, Feet, Meters

File Formats

Web GIS

Readable

Format

Geo-referencingGeometry

Data

Attribute

Data

Flow Diagram for Task 1: Handling Geospatial Data

Task 1 : Handling Geospatial Data

ESRI Shapefile Standard Feature Must convert to proprietary format via third party tool

Must convert to proprietary format via included tool

Standard Feature

TIFF Standard Feature Standard Feature Standard Feature Standard Feature

ODBC Standard Feature Standard Feature Standard Feature Standard Feature

Coordinate System/ Georeferencing

Does not require any inputs for reference system

Reference system designated using Geoset Manager

Reference system designated using SDF Loader

Reference system designated using separate program

Handling Geospatial Data – Observations

Displaying Map Features

Web GIS must be able to display and label standard map features relative to scale and category.

• Polygons (Municipalities vs. Built-up Areas)– Different land areas of cities can be grouped into distinct classes– At large scales, cities represented as polygons– Different classifications imply that polygon map features must be represented using

color fills, hatched patterns, a patterned stroke, or some other means of clearly differentiating categories

– As scale changes, Web GIS must be able to collapse certain polygon features into points

• Lines (Transportation Networks)– Interstates, state highways, farm-to-market roadways represent nominal

classification. Web GIS software must be able to generate linear map features with different line widths and colors

• Static Lettering/ Labeling– Labels must not scale when the Web GIS map’s scale is changed– Users/developers must have control over typeface, font size, and font color

• Generalization– Ensures legibility and correct visual communication of geographic information at

every scale of display.– Ensures features resemble actual dimensions of the geometric objects

Flow Diagram for Task 2: Displaying Map Features

Web GIS

Readable

Format

Geometry

Data

Points

Lines

Polygons

Polygons

Infrastructure

Built-up Areas

Municipalities

Vis

ualiz

atio

n

Sta

tic L

ette

ring

Gen

eral

izat

ion

Webmap

Task 2 : Displaying Map Features

Solid/Hatch Fill Allows solid fill;Cannot generate hatched fill

Allows for solid fill; Allows for hatched fill

Allows for solid fill; Allows for hatched fill

Allows for solid fill; Cannot generate hatched fill

Color Limited selection of named colors

Limited selection of named colors

HTML colors Integrates color selection from the Windows color palette

Font properties Possible to place labels using fonts that are hard to read; size independent of map units; cannot draw boxes around labels

Possible to place labels using fonts that are hard to read; size independent of map units;boxes can be drawn around labels

Possible to place labels using fonts that are hard to read; size scaled to map units;boxes can be drawn around labels

Possible to place labels using fonts that are hard to read; size scaled to map units;cannot draw boxes around labels

Text Placement Places labels at the best place.

Fixed positioning for labels

Allows some control for the positioning of labels

Cannot position names on map features

Generalization Cannot handle different views for different scales

Cannot handle different views for different scales

A different map view for each scale interval

Cannot handle different views for different scales

Road Network Offers a moderate selection of line styles (less than MapGuide, more than Geomedia)

Offers a moderate selection of line styles (less than MapGuide, more than Geomedia)

Most options for drawing composite lines

Fewest options for drawing lines

Displaying Map Features – Observations

Displaying Thematic/Attribute Data

• Web GIS software must be able to generate chorochromatic maps– Each polygon (e.g. city enclosure) must have its own color fill

based on something like a nominal classification of a unique variable

• Web GIS software must be able to generate choropleth maps– Thematic datasets contain statistics about physical environment,

population, economics, etc.– Some data sets provide relative values, others offer absolute

values– Software must be able to generate proportional symbol maps to

represent absolute values and to generate these types of maps to represent the relative values correctly

Geometry

Data

Attribute

Data

Classification

Nominal

Interval

Task 3 : Displaying Thematic/Attribute DataWeb GIS

Readable

Format Thematic

Webmap

Choropleth Map

Chorochromatic Map

Proportional Symbol Map

Qualitative

data

Quantitative

data

Flow Diagram for Task 3: Displaying Attribute Data

Classification Selectable classification scheme

Does not support classification schemes

Does not easily support classification schemes

Does not support classification schemes

Chorochromatic Map

Can be generated using a simple user interface

Requires some ASP/VB Script code

Requires some ASP/VB Script code

Requires some ASP/VB Script code

Chloropleth Map Can be generated using a simple user interface

Requires some ASP/VB Script code

Requires some ASP/VB Script code

Requires some ASP/VB Script code

Proportional Symbol Map

Can be generated using a simple user interface

Very difficult to generate these kinds of maps

Requires some ASP/VB Script code

Very difficult to generate these kinds of maps

Displaying Thematic Data – Observations

Outputting Hardcopy Maps

• Web GIS software must allow for printing a specific view of the Web Map, together with the marginal information

• This requires server-side control over the layout of the document, so users can print maps according to pre-defined layout that assures correct hardcopy map output.

Hardcopy Output

May omit scale of legend – requires some programming

No standard tools to do this

Provides detailed printing; programs allow custom printing

Users have little control over the print functions.

Output of Hardcopy Maps – Observations

• External Identification: Scale, Co-ordinates, and Index Map– Users need to know their location in the geospatial database and where

to go– Mouse pointer’s location in map should disclose map co-ordinates– Scale bars should be implemented

• Internal Identification: Map Legend– Most important interface to the web map– Lists the names of the themes in the map and their cartographic

visualization– Must be automatically generated

• Query Tools– Users need to interact with the Web presentations by asking questions– Users need to know values of variables or what is a particular map

element’s properties or statistics.

Transferring Geographical Knowledge

Map Scale No means are provided to indicate scale for a thin client.

Uses a dialog box to inform the user of the map units in terms of the screen width

Client-side scale not provided

Automatically displays a scale bar

Coordinates Mouse Pointer

User clicks on image and screen location converted to map coordinates

User clicks on image and screen location converted to map coordinates

Does not provide a means to translate mouse position to map coordinates

Does not provide a means to translate mouse position to map coordinates

Index Map Standard function Does not do this Does not do this Does not do this

Legend No straightforward means to generate map legend for thin-client.

Contains some options to implement a simple, restricted legend.

No straightforward means to generate map legend for thin-client.

No straightforward means to generate map legend for thin-client.

Query Tools Takes too long for users to change view of Webmap to see a particular location

Takes too long for users to change view of Webmap to see a particular location

Marginal at best. More difficult to use than Arc and MapXtreme.

Lack of clickable features makes software unsuitable to develop query tool

Transferring Geographical Knowledge – Observations

• Thematic datasets contain statistics about various topics.• Example:

– How many people live in the built-up area of a particular municipality and are within 1/8 mile of an interstate highway assuming 80% of the population of a city lives within the built-up area and assuming that the population is equally distributed within this area?

• Web GIS software answers this question through answers to a sequence of more specific questions:

– What is the name of the city and the interstate hwy on the map?– How large is the distance of 1/8 mi on the Web map?– Make a buffer of 1/8 mi around the highway– What is the area of this buffering surrounding the highway up to 1/8 mi on

both sides?– What part of the city intersects this area?– How many people live within this area?

• Users must be able to measure distances in the Web map between map features.

• Users must be able to make buffers around map features.

Geometric Map Comparison

Task 6 : Geometric Map Comparison

Flow Diagram for Task 6: Geometric Map Comparison

Measuring Distances

Buffering

Measuring Distances

Requires extensive scripting.

Missing Measuring tool is a standard.

Requires moderate scripting.

Buffering Requires extensive scripting

Missing Buffer tool is a standard option.

Requires extensive scripting.

Geometric Map Comparison – Observations

• Web maps function as interactive working documents and play important roles in supporting geospatial decision making

• Joining different geospatial data sets is a common operation for individual research• Multiple options of visualization of the same thematic attribute must be enabled by the

Web mapping application by means of “re-expression” tools. Since the map is linked to a database, the GIS visualization is altered easily, resulting in a new map type. These “re-expression” tools must facilitate visualization of both relative and absolute values of available datasets to provide correct images of the datasets

• Clicking an object in a particular view shows its geospatial relations to other objects and representations in all the other views.

• Web GIS software must be able to add links to map features.• Bookmarking must also be supported.• Users should be able to hyperlink from one Web document to another. This technique

enables additional presentations of text, images, video, etc.• Clickable map features must have alternative visualization from non-clickable map

features in the same theme and the mouse pointer icon must change as it is placed over a clickable map feature.

• When users are looking at a particular Web document and want to be able to quickly get back to it later, they should be able to create a bookmark for it. A bookmark should be saved as URL-link w/in the Web browser.

Integrating the Web

Add hyperlink Thick clients can add hyperlinks to map features in Webmaps.

Thick clients can add hyperlinks to map features in Webmaps.

Thick clients can add hyperlinks to map features in Webmaps.

Thick clients can add hyperlinks to map features in Webmaps.

Clickability Users can only hyperlink after selecting a hyperlink tool; no visual cues that indicate whether a feature is clickable.

Users can only hyperlink after selecting a hyperlink tool; no visual cues that indicate whether a feature is clickable.

Serve clickable map features at all times.

Serve clickable map features at all times.

Bookmarking Does not support. Difficult to do. Requires considerable scripting.

Only package to offer client-side bookmarking.

Does not support.

Integrating the Web – Observations

Conclusions

• Autodesk MapGuide appears to offer the most functionality of all the tools.

• ArcIMS is the best tool at displaying thematic data and for transferring geographical knowledge.

• Autodesk supports the best tools for displaying map features.

• Autodesk has the best hardcopy function.• Autodesk is the best at geometric map comparison.• Autodesk is the best at integrating with the Web.• Autodesk is the best tool for most kinds of analysis

involving database queries and report generation. ArcIMS is the best tool for public (thematic) presentation of maps!