Google has released its Maps app for the iPhone, in the wake of complaints about Apple's software.
Apple controversially replaced the search giant's mapping service with its own when it released its latest handset, the iPhone 5.
The move was widely criticised after numerous mistakes were found in Apple Maps's search results.
Google's app introduces functions previously restricted to Android devices.
One analyst said it would prove popular, but added that Nokia still posed a challenge.
The Finnish company recently launched its own free maps app for the iPhone.
The firms are motivated in part by a desire to gather data automatically generated by handsets using their respective software, as well as users' own feedback.
This allows them to fine-tune their services and improve the accuracy of features such as traffic status updates.
Android's advantage
Features Google has introduced that were not available in its earlier iPhone app include:
Voice guided turn-by-turn directions, with estimated travel times.
Indoor panoramic images of buildings that have signed up to its Street View Business Photos service
3D representations of the outlines of buildings that can be viewed from different angles
Vector-based graphics based on mathematical lines and points rather than pre-created bitmap graphics, making it quicker to zoom in and out of an area.
Among the facilities Google's iPhone app lacks that are present in its Android equivalent are indoor maps, the ability to download maps for offline viewing, and voice search.
However, over time, project manager Kai Hansen told the BBC that what was on one platform should be on the other.
"The goal is clearly to make it as unified and consistent an experience as possible," he said.
Ground Truth
One area Apple's own software still has an edge is its integration of Flyover which offers interactive photo-realistic views of selected cities using 3D-rendered graphics within its maps app.
Google offers a similar facility via Google Earth which is promoted in its main maps app, but involves switching into a separate program.
However, for many users the key feature will be the level of accuracy that Google offers.
Since 2008, the firm's Ground Truth project has mashed together licensed data with information gathered by its own fleet of Street View cars and bicycles.
The images and sensor data they collect are analysed by computers and humans to identify street signs, business names, road junctions and other key features. To date, more than five million miles (eight million km) of roads across 45 countries have been covered.
This information is supplemented by the public filing their own reports. iPhone users are encouraged to do likewise by shaking their handsets to activate a feedback function.
"Google Maps, as much as any other map application, lives from the data that we receive," Mr Hansen explained.
"If a road is closed for the next six months, or a road was opened two days ago - these are things that somebody who lives next to the road immediately notices, but if you're not in the area it becomes hard to know.
"The more we can give you the ability to let us know about things that are changing on the map, the more other users will benefit from that corrected information."
He added that once operators verify these reports, changes can be made "within minutes, rather than hours".
Apple is also seeking to improve its own data through user feedback, but risks having less to work with if iPhone users switch to another product.
There had been speculation Apple would reject Google's app from its store for this reason.
But since iPhone sales are at the heart of Apple's fortunes, it may have felt it had more to lose than gain by allowing rival Android handsets to offer a popular app it lacked.
'Neutral' Nokia
Google's launch will also have consequences for Nokia, which recently launched its own Here Maps app on iOS.
The European firm's location division is decades older than Google's, and also has a strong reputation for accuracy.
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