I've been using online maps for quite a while and I've noticed that the map coverage for Malaysia has improved over the years but freely-available geocoding services covering Malaysian city streets are still sorely lacking.
Multimap
However, one mapping service comes close. It's Multimap (now a wholly-owned Microsoft subsidiary). While street-level geocoding support for KL is not quite there yet, there's postcode geocoding. The street map quality is much more detailed than the one in Google Maps, MapQuest or Microsoft Virtual Earth.
In Multimap, you can view the lot number of homes/buildings and names of street landmarks. However, Multimap's aerial/satellite view (which leverages on Microsoft Virtual Earth) is not the best for Malaysia. In that respect, Google Maps offers much higher-resolution visuals.
StreetDirectory.net.my
Another cool street mapping service for KL is found on streetdirectory.net.my. You can enter street names or even building names. It even lists how far away a location is from nearby landmarks such as banks, restaurants, monorail stations and even pubs!
Google Earth and Google Maps
For virtual 3D visualization of KL, there is Google Earth (essentially 2D Google Maps mapped on a 3D terrain). With Google Earth 4.3, you can view photo-realistic buildings for several cities around the world. As for KL, you'll only find the Petronas Twin Towers in 3D though.
One thing to note is that the satellite images in Google Maps (hence Google Earth) for most parts of KL are not very recent. Most of the image tiles date back to 2005. However, Putrajaya has more recent visuals (May 2007).
I'm looking forward to the day when we can enter a Malaysian street address in Google Maps or Google Earth and the specific location is returned. At the moment Google Maps supplements the search results with community-tagged locations. Quite often, there's too much redundancy in community-based results and it only adds to lots of noise.
So while we wait for real geocoding service from Google on Malaysia, we'll make do with the services mentioned above.
