Problem

Availability of location based service, and the actual location of the handset must be easily and accurately communicated.

Location can present more that just a pinpoint on a map. Direction can be indicated organically, with the pointer and by rotating the map to match direction of travel, as well as with compasses. Speed and other attributes (e.g. height, relative position) can also be displayed.

Solution

Mobile devices have numerous methods of retrieving location information. These are listed in, approximately, less to more precision, but are not necessarily better or worse otherwise.

Does that mean that the device's range is 1,500 m from the Cell's location (radius)?

Not clear what you mean by "inaccuracies"?

Both of these currently use the "cell" (or network identifier) and triangulation methods described above.

They are both relatively more rare, and often are supported by third party software or individual services (which may have specific capabilities), and are not universally implemented on the handset. There are no reliable, independently verified numbers on the real-world precision, but tests of WiFi triangulation alone have gone down to inches. On the other hand, poor network identification has led to placing users on the wrong continent.

Each of these must be understood, be able to be used (as long as the hardware is available) by the system and by each application, and communicate the correct degree of precision and accuracy.

An understanding of the difference between precision and accuracy is also crucial. In brief: precision is the number of decimal places you measure something to; accuracy is how correct it is. The less accurate you think your measurement is, the less precise you should report it.

Privacy and security concerns are beyond the scope of this book, but must be considered when designing location based services. In many countries, there are legislative or regulatory restrictions on enabling and use of location services, so notification of background tracking is a legal requirement, not just best practice.

Location is not the same as Orientation or other types of position information. When these must be communicated -- as for augmented reality -- they are generally deeply integral to the visualization and interactive design of the application. No distinct patterns yet exist for these behaviors, but best practices from aviation may serve to guide designs.

Variations

Location service is often used as a background service, or promote smarter ambient computing,. When directly referred to, it may only be momentarily switched to while other tasks occupy the remaining time. Therefore, both explicit and background indicators cases may be present not just in the same system, but at the same time.

Settings, including installation of applications using location services, must also take into account these principles, especially those of privacy and awareness.

Though this pattern discusses such behaviors and features on a mobile device, they may also be used for remote devices in much the same manner. "Child trackers" and similar functions may be used from another mobile device or from desktop computers to track a remote mobile device. In this case, both the viewing terminal and the mobile device must both consider the display and behavior attributes of this pattern.

When information is not available, such as speed and direction of travel, it should generally not be shown at all, instead of simply being zeroed out. Precision must always be shown with a true-to-scale error scale circle, and numerical precision whenever possible.

Interaction Details

Indicators of state are generally only present in the Annunciator Row and cannot be interacted with. A system setting should be made available to control the use of GPS, WiFi and other controls, as well as to set privacy controls for sharing and how much automatic (vs. manual) control is allowed over these systems.

An easy method must be provided to access this control, without drilling into multiple sub-menus. Whenever possible, add this control shortcut to any application that uses location services. The control may also be added as an interactive Icon on the Idle Screen for access from any application, or so the user may manually enable the service before it is needed.

Whenever possible, applications or services which are best with location should automatically enable the required hardware. OS level restrictions or user settings may interfere with this behavior, and require user intervention each time. If so, an interstitial Pop-Up is often the best way to request this.

When the Pop-Up itself is restricted from offering a function to enable the GPS (or other hardware), use it sparingly, as a reminder to the user instead, and provide a link to the appropriate settings panel. When settings are changed, always return the user to the originally-requested application.

Only use the precision required for the task at hand. Weather, for example, rarely requires more than city-level precision. The GPS is not required for basic conditions and forecast information.

On the other hand, always present the most relevant details for each view. If the user chooses to view a local radar map, they should not be required to know their location but should be presented it systematically. The weather application may have to turn on and off various location services as the application is used, and should not enable all services when it is opened, or get by with only the minimal set and present less than optimal information.

Icons to denote location services are not just optional variations, but can imply different meanings. The crosshair is a standard used not just to denote location enabling, but that the mobile handset sends it’s location to the operator, for e911 and other purposes. The satellite dish and satellite denote GPS specifically, and may be used to denote other conditons. For example, the dish may imply the device requests service, and the satellite only appears when a link is established.

Presentation Details

When location service is enabled, this should be shown in the Annunciator Row, generally as an icon. The location icon (crosshair) has come to mean GPS is enabled, so there may be challenges in communicating other types of location services. GPS can use other types of icons, such as a satellite dish. GPS requires a short time to find position, and can loose position due to interference, clutter or other conditions, and must display the current status. Generally, animating the satellite dish (implying "scanning for service") works well.

Avoid duplicating indicators. If in the Annunciator Row, there is generally no need to also include such indicators within an application. This is another good reason to preserve Annunciator Row display, instead of loading applications full-screen.

For explicit graphic display of location, such as on a map, a cursor will be used to denote the current position. Note that this is actually the centroid of the CEP or circular error of probability. A probability threshold is programatically established; based on the technology used to determine location, the device is almost certainly located within this circle. (Note, it is impossible to absolutely determine location, hence the "probability" prhasing, but this is not terribly important for general discussions).

This CEP circle should be displayed, with the cursor at the center, as a visual method of communicating the precision of the location technology. Unless additional precision is needed but is currently unavailable, the default view should hide the CEP circle from the user. For a weather map, for example, the default zoom level should be large enough that a 100 m CEP is smaller than the cursor, so disappears under it. Good selection of map zoom level also helps communicate the degree of precision available.

Coordinates and other location information, when relevant and useful, should be presented on screen in an easy to read format. Multiple formats may be presented at once, as shown here. Here, many digits have been removed, in the interest of using only the degree of precision available.

When the display is zoomed such that the CEP circle is at least 10 times the size of the cursor, or the edge is partly or entirely outside the viewport, an explicit display of precision (discussed below) should be printed adjacent to the cursor.

An even greater pitfall in the display of precision information is with printed location, especially in coordinate systems. Whenever possible, use standard, well-understood nomenclature. Avoid printing the location when not useful; lat/long is difficult to interpret and very few general users will understand it.

Precision also must be accounted for. For this example, the MGRS coordinate system will be employed as it is based on simple measurements from a regional baseline. This is unlikely to be employed in general consumer applications, however. A complete location to 1 meter precision is listed as:

15S UD 12345 67890

However, most location technologies, in most instances, cannot give such precision. Digits should be removed until only the correct level of precision is shown. For example, if using cell sector, with precision in the 100 m range, only display

15S UD 123 678

The last digit will always be of less precision than the others, and even when displayed digitally can be used like that on a dial or scale. Simply restrict the display to only the 5 or 0 digits.

Precision should be explicitly displayed when coordinates are printed. Use the existing settings for units of measure, but scale them appropriately. In the following examples, the user has set their navigation tool to use miles.

Note that the term "precision" is not well understood, so is often replaced with "accuracy" in general communications, as in the examples above, although it is not strictly true.

Addresses, likewise, should only be displayed when that level of precision is available. Otherwise use existing best practices for general location:

Only display the larger scale information such as state and country when needed. When moving between two areas only a few miles apart, the default location display should probably just be the street address portion. The same filtering logic should be used for coordinate systems, when applicable. While Lat/Long is a global system, UTM and MGRS are divided into regions; the "15S UD" portion in the example above can be made much less prominent, as most precision navigation is not also global navigation, so it will not be used as much as the remainder of the displayed coordinates.

Direction of travel should only be displayed when available, and should only display to the degree known. Generally, the cursor will be a pointer to assist with this. For free standing displays, when users will understand, display bearing in degrees, and by named directions (north-east) but degrade to cardinal directions as the system's understanding becomes more poor.

Cardinal directions (e.g. "North") can imply precision if simply printed on the screen; use graphic displays (either dials or circular Tapes) to communicate the degree of precision available, make small changes in bearing angle visible to the user and make the display more glanceable.

When direction of travel cannot be determined (there is no compass and the device is not moving), display no direction of travel indicator, or an icon indicating it is unknown. The cursor may change to circle, or otherwise become blunted to reduce or remove the implication that direction is known. Do not display the last direction, as this is likely to be spurious data arising from loss of signal or stopping.

When direction of travel is available, orient the map so direction of travel is forward, or up. If there is a specific reason not to do this by default, provide a function so the user can switch to this mode.

Antipatterns

Never equate "location" with "GPS," especially to the degree that a location aware service or application may only launch when the GPS is enabled.

Never display or imply precision that is not available. Avoid the use of crosshairs and other implied attributes, even if a CEP circle is displayed as well.

Examples