3.2 Smart Map Browsing

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3.2 Smart Map Browsing

Using the foregoing analysis results as a base, the objective of the following section is to: a) devise a definion of the term Smart Map Browsing, b) derive its properties, and c) outline its potential.

The expression Smart Map Browsing is not used in current literature and will be further defined and elaborated in this thesis.

3.2.1 Term

The definition for the term Smart Map Browsing is based on the ISO standard for usability (see Section 2.2.1):

3.2.2 Characteristics

The current state of technology related to Smart Map Browsing can be described in more detail using two categories - GUI components and Pan/Zoom properties. It should be noted that because these characteristics are based on the current state of technology (effectively a Smart Map Browsing 1.0), medium-term modifications will be required as newer technology becomes avaialble.

A) GUI Components

Main Map

In web applications where the map forms the main part of the application (as opposed to applications where maps are merely useful »additions« to other functions), the map should occupy the main part of the application's interface. A seamless change in map size (e.g. by moving map edges) allows the user to set a map according to his/her individual requirements. The ability to adjust the map to the current browser size is is also considered a positive Smart Map Browsing feature.
One usability aspect in web mapping applications that should not be overlooked is map design. An attractive map layout, easy-to-read signatures, symbols and lettering, intuitive colors in attractive combinations and a well-selected graphic picture density - they all have a positive influence on the attractiveness of a web map [R�ber u. Jenny 2003].

Overview Map

The ability to navigate in the overview map is an important criteria in Smart Map Browsing. The click/double-click along with Drag&Drop drags the selected section in the reference map. Following the intereaction with the overview map the selected section is always re-centered. This is an important feature for maintaing the interactive relationship with the user, as well as to ensure his/her orientation during this process.
By panning the main map, the overview map is also immediately adjusted to the new location. In this case, a simultaneous panning action (animated panning) involving the main and overview map is considered ideal as the user is provided with the new map position but does not lose track of the overall position.
The overview map is also adjusted according to the zoom level in the main map. In this case the scale used is always larger than the one used in the main map (by a defined factor) so that the overview map retains its ability to serve as an »overview« for the user.
The feature allowing the minimization of the overview map is considered useful. Placing it within the main map means more available space for the main map; at the same time this location of the overview map places it within the user's center of attention.
A further improvement to usability would be to also display the active layers in the main map in the overview map.

Layer Control

When a layer is turned on/off, the map is automatically updated (no confirmation required). This feature is an important characteristic of Smart Map Browsing. The ability to minimize the overview enables the user to turn his/her full attention to the map at hand. In addition, the ability to change the layer sequence and to integrate a legend into the layer control are also considered useful (depending on the application).

Legends

Legends should be as succinct as possible and directly related to the map contents. The components of a legend should be ordered according to their significance, grouped with similar elements and displayed accordingly [R�ber u. Jenny 2003]. Again, the ability to minimize the legend enables the user to get a better view of the map at hand.

Scale

Scale indicators or bars are only useful if they are recalculated for each zoom level [R�ber u. Jenny 2003]. A scale bar should be available during Map Browsing so that estimates of distances can be done with the naked eye. The use of bars is recommended (particularly for web applications with »inexperienced« map users) and is preferred over the use of scale indicators. Ideally, the bar is displayed semi-transparently within the map.

Toolbar

Overly extensive toolbars can have a negative effect on the usability of an application. Limiting the toolbar to the advanced query and analysis functions is advisable as it would result in »smart« Map Browsing. Simple zooming and panning functions are ideally done with a pan/zoom bar or similar 'intuitive' pan/zoom features (such as mouse wheel, double-click). Another important factor in smooth Map Browsing is the ability to switch between panning and zooming without having to first activate the respective tool.
In so far that it is considered useful, a mouse cursor should visually reflect the user's tool choice (by changing the cursor image) so as to confirm the selection.
In this respect the zoom history feature is a useful Smart Map Browsing feature. This feature allows a user to un/redo recently-made panning or zooming activities.

Zoom Bar

One of the most significant Smart Map Browsing feature is the zoom bar. It offers a high degree of interactivity and a good visual indicator of the current zoom level relative to available zoom levels.
The term continuous zooming denotes the ability to scale a map 'on the fly' by moving the zoom slider. The map is only loaded to the selected scale when the slider is released. This feature increases the user's navigational ability and serves as a good example of Smart Map Browsing.

Pan Navigation Panel

The pan navigation panel offers intuitive and precise panning. Integrating the panel into a Pan/Zoom bar is preferable to locating it on the map edge because navigation »by mouse« is made simpler and quicker.

According to [R�ber u. Jenny 2003] navigation and control elements in web mapping applications should be self-explanatory and efficient. They should also be logically grouped to facilitate the use of the web mapping program. The user should be able to quickly find the required function instead of being overwhelmed by the available functions. The navigation of a map containing many different elements is quite complicated and requires a fairly steep learning curve. As a result, a map navigation control pad which is intuitive should be the main focus, while the more demanding functions should be simplified as much as possible or at least reduced to a minimum [R�ber u. Jenny 2003].

It it not imperative to place navigation components outside the map view. The advantage of placing the controls inside the map is that the user is always aware of the available options, as they are in plain view (and easily noticed) rather than being relegated to the side. Having a correspondingly attractive representation of the controls is also beneficial [R�ber u. Jenny 2003].

B) Pan/Zoom Characteristics

Zooming with double-click

Zooming with double-clicking on the map enables a smooth transition between panning and zooming without having to separately switch to the corresponding controls. This feature increases the intuitive nature of the application and is therefore defined as a characteristic of Smart Map Browsing.

Zooming with mouse wheel

Similar to double-click zooming, zooming via mouse wheel also increases the usability of the application by ensuring a smooth transition into zoom mode.
Accordingly, we speak of a Smart Map Browsing feature when the geographic position shown by the mouse wheel during the zoom process is at the same pixel position after the zoom is completed. On the other hand, zooming that centres the map according to the position of the mouse cursor, or does not take into account the actual cursor position, is not along expected lines and therefore not considered part of a Smart Map Browsing definition.

Zooming with zoom box

The ability to zoom with a pull-out zoom box has become a standard feature in most web mapping application - a feature most users would now expect to see. Along with a zoom box button on the toolbar it should also be possible to draw the zoom box by pressing the Shift-key. In addition, a unicolour, semi-transparent shading of the zoomed area provides the user with a visual confirmation of his choice.
This useful feature is considered a critical element of Smart Map Browsing.

Zooming/Panning with keyboard

Simple navigation manouveurs should be executable with the plus, minus or arrow keys. An extended, intuitive keypad for the pan function is considered beneficial to usability (some of the more obvious choices for rudimentary map re-positioning are Home, End, Page ↑, Page ↓).

Zoom Levels

Zoom level intervals should be clearly delineated. The zooming function is deactivated once the maximum or minimum zoom level is reached, with the corresponding buttons showing that the zooming function is no longer active. Displaying the potential zoom depth on a zoom bar is also helpful to the user's orientation while viewing the map.

Zoom Reset

A user would expect to be able to reset the map to its maximum dimensions by using a zoom reset function. Following the principles of usability, whereby similar elements are grouped logically, a similar integration of the zoom reset buttons into the pan/zoom bar is recommended. This means that all zoom and pan functions can be located outside of the toolbar (see also (A) GUI Components).

Animation

Animation in web maps is done for several reasons: To increase the user's attention level, to direct attention to specific objects, to increase the user's orientation during the navigation process or to lead him/her through a specific topic. There are two different types of animation: temporal and non-temporal [Dickmann 2004][R�ber u. Jenny 2003].

Temporal animation displays spatial changes which occured in a specific period of time [Dickmann 2004][R�ber u. Jenny 2003]. An example of temporal animation is the display of population growth of a city in, say, the last century. The user should be able to interact with the animation by using self-explanatory navigation elements. It is easier to display complex data with time flow. These types of animations should take place within the confines of the main map and not replace a web mapping application's interactive Map Browsing.

Non-temporal animation displays spatial data of one concrete point in time with different illustrations [Dickmann 2004][R�ber u. Jenny 2003]. An example of non-temporal animation would be an automatic »ZoomTo« feature, whereby the user is led to a specific location through the use of non-temporal animation. This in combination with map navigation controls results in very dynamic pan and zoom properties, which are described as animated panning and animated zooming in [OpenLayers b]. The user's orientation and ability to judge distances ie. scale is not hindered.

Cartographic animations increase the user's attention and add considerable value to the map. Animations (within a reasonable range) are an important characteristic of Smart Map Browsing.

Tiling

One of the most fundamental characteristics of Smart Map Browsing is the tiling of maps. To reduce the cumbersome computing time associated with servers, a client-side tiling is to be preferred over server-side processes (see Section 2.3.5). Provable measurements were not carried out. Ideally, tiling results in an absolutey smooth (ie. without delay) map movement. During zooming the tiles are assembled in a spiral or star-like manner, beginning from the middle of the map. This dynamic loading process provides the user with a visible confirmation of the map loading process.

Load Time

The most important criteria of a web page is its load time [Nielsen 2000]. Here a distinction between objective and subjective load time needs to be made. The former is the time actually required to load a page; the latter refers to the user's personal impression of time while the page is loading. According to Jakob Nielsen the objective load time should not exceed eight seconds. Anything above this value negatively affects the usability of a web application.
In the context of web mapping applications, the most important issue is the time required for a user to be able to view a map. The load time required for the complete page, including all details and if applicable, pre-loaded tiles for the non-visible area, is less significant in this case [Nielsen 2000]. Ideally there is no time delay during a drag procedure (see Tiling). A map constructed with sequentially appearing tiles appears to take less time (ie. has a faster subjective load time) than an untiled map which is shown only when the process is completed. Tile Caches can be used to increase the objective load time during tiling. A more detailed discussion follows in the next section.

Inherent in the definition of Smart Map Browsing is the user's ability to interact with a web mapping application in a variety of ways. At the same time, the usability of each interaction is of paramount importance, that is, the performance of the component(s) should always conform to expectations.

3.2.3 Potential

The main characteristics of Smart Map Browsing along with their potential in the web mapping area are featured below:

Tiling (client-side tiling only) is without doubt one of the most significant characteristics of Smart Map Browsing, with great potential for user-friendly web mapping applications. However, tiling on its own (see Chapter 2.3.5) does not guarantee good Smart Map Browsing. Even the highest-performance application cannot offer good usability if the response time of the map server is very long. Tiling does not predict the objective load times of tiles. In the spirit of the Smart Map Browsing definition, the goal should be to reduce objective load times as much as possible.

One solution is server-side Tile Caching (client-side caching will not be discussed). Here the tiles are kept on the server in the form of readily rendered graphics, thereby reducing the response time of the map server: When a client requests a map, the server does not have to generate the map, instead it accesses the finished tiles (usually stored in the file system) and sends them to the client in a considerably shorter time frame. For this purpose, the tiles must be of uniform size and available in a pre-defined tile grid.
WMS Tile Caching¹⁸ or WMS-Cached - in short, WMS-C - is representative of an initial recommendation on how such a standard could look based on the OGC WMS specifications. A more detailed suggestion for a standardized solution is described in the WMS Tiling Client Recommendation¹⁹, a result of the Tiling Discussion Group at the FOSS4G Conference 2006²⁰ in Lausanne. Based on this recommendation the US company MetaCarta²¹ has developed the implementation of TileCache²² - a WMS-C compliant server, available under the BSD license. TileCache is a Python-based WMS/TMS²³ server containing mechanisms for the rendering and caching of tiles. In the most simple scenario, TileCache can create its own local cache of (all) tiles on the hard drive. It accomplishes this by means of write access to the hard drive, the ability to execute Python CGI scripts and the designation of a chosen WMS server. The tiles are subsequently requested by a WMS-C or TMS-supporting client (such as OpenLayers). TileCache is said to speed up WMS requests by a factor of 10 to 100. The use of TileCache under mod_python²⁴ supports more than 300 requests per second [MetaCarta].
Server-side tile caching offers significant potential for the further development of Smart Map Browsing in web mapping applications. Despite the short history and still outstanding OGC standardization of WMS-C, noticeable progress in the load times of WMS maps has been made. Accordingly, tile caching promises to become a fundamental feature of Smart Map Browsing.

By turning the focus to the navigational elements of web mapping applications the Smart Map Browsing ability of the Zoom Bar is noteworthy. The analysis (see Section 3.1) shows a noticeably improved usability in the four applications which feature this type of component. The zoom bar in combination with a pan navigation panel and a zoom reset button enables an implementation of the above-mentioned usability guidelines. The defined aspects of the zoom depth orientation (see Section 3.2.2) offer additional opportunities to influence the concept of usability.
In conclusion, the use of a zoom bar offers great future potential.

Closely connected to this development are the very recent and innovative attempts at animating different navigational features. Animated panning and animated zooming are Smart Map Browsing features which are currently implemented in only three of the analyzed applications.
Animated panning, in conjunction with tiling, offers a good method of assisting users to go from point A to B by way of an animated and no-delay process. Similar to Drag&Drop panning, this process demonstrates to the user that the viewed map selection is only a part of a whole, seamlessly connected map - a clear advantage in preserving the user's orientation in the viewing process.
Essentially, the animated zooming feature is an automatic zooming process that animates the transition from zoom level A to level B. During the zooming process the map is scaled and redrawn once zooming level B is reached. This type of animation permits the zooming in and out of the map at one or more zoom levels. animated panning and zooming is also a possibility.
Furthermore, the animated zooming feature implies an additional function: Moving the slider of a zoom bar results in a seamless rescaling (up or down) of the current map. This is an example of manual non-temporal animation.
An accepted glossary term for zooming animations in web mapping applications does not yet exist. Given the similarity to animated panning characteristics the term animated zooming seems a plausible choice. On the other hand, Google Maps, uses the term continuous zooming to denote zooming animation per mouse wheel (currently only in Windows operating systems). In this discussion the term animated zooming is used to denote automatic zoom processes (initiated by e.g. click, double-click, mouse wheel or zoom box). Furthermore, animated zooming is used as a collective term describing all animation-supporting zoom processes in web mapping applications, including continuous zooming (used interchangeably with seamless zooming).
It stands to reason that these two recent features (animated panning und zooming) will play a signficant role in the further development of Smart Map Browsing. Currently, some performance problems (caused by limited band width or client hardware) can occur with extensive animation, which could negatively influence usability. At the same time, the future potential of these extensions is clearly recognized, and it is conceivable that they will soon become an intrinsic part of any web mapping application.

3.2 Smart Map Browsing

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