Geography Reference
In-Depth Information
map that has ever been developed. Overlaying features on top of these maps
provides a familiar and comfortable frame of reference for the map user. As a
result, maps made in other ways, with other software, are viewed as unfamiliar and
even foreign. This includes maps created with popular GIS software such as ESRI
'
s
ArcGIS.
Mapping APIs are closely integrated with map tiling. Used since the early days
of the World Wide Web, image tiling speeds the delivery of graphics through the
Internet. In comparison to text, images require more storage and therefore take
longer to download. A solution is to divide the image into smaller segments, or tiles,
and send each tile individually through the Internet. These smaller files often travel
faster because each can take a different route to the destination computer. On the
receiving end, the tiles are reassembled in their proper location on the web page.
With a moderately fast Internet connection, all of this occurs so quickly that the user
rarely notices that the image is actually composed of square pieces. With slower
connections, the individual tiles are clearly evident—sometimes painfully so. In
combination with AJAX, an alternative way of interacting with the server, the tiling
of maps facilitates MSP maps by allowing maps to be easily panned and zoomed. In
evaluating mapping APIs, we begin by reviewing some of the different APIs that
are currently available.
Comparison of Application Programmer Interfaces
for Mapping
Google Maps API
Introduced soon after Google Maps in 2005, the Google Maps API is by far the most
commonly used. The API consists of a series of functions that control the appear-
ance of the map, including its scale and location, and any added information in the
form of points, lines or areas and associated descriptions. The use of Google Maps
API is essentially free, provided the site does not charge for access. Google limits
the number of maps that can be served: A site cannot generate more than 25,000
map loads a day for 90 consecutive days. A map load is one map displayed with the
Google Maps API. Once loaded, the degree to which a user interacts with a map—
panning or zooming—has no impact on the map load number. It would be
extremely difficult for a non-institutional user of the Google Maps API to reach
25,000 daily map loads. Even if a site were to go “viral” with a topic that generates
considerable interest, it would need to sustain 25,000 map loads per day for
90 consecutive days. Viral topics are fickle and have a much shorter lifespan.
The default Google marker is an upside-down raindrop symbol but a large
number of alternative symbols are available. It is even possible to design symbols
using a program like Adobe Photoshop
. The code in Fig.
1
places the basic
Google marker at the center of the map. The event.addlistener option sets the zoom
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