Google Maps API 3

CHAPTER 1 ■ INTRODUCING THE GOOGLE MAPS API
The main legacy pitfall was the architecture of the old API. It was built using a synchronous model.
Because of this, the browser had to download and run a lot of scripts sequentially before it could actually
display the map. A major goal with the new API was to modularize it so that the necessary code is loaded
first, displaying the map, and everything else is loaded later.
The result of the efforts of the API team is an API that is significantly faster on mobile platforms such
as iPhone and Android and also a lot faster on desktop platforms.
■ Tip If you want to know more about how the new API was built and what led to those decisions, I recommend
you watch the first part of the talk, Performance Tips for Geo API Mashups, from the 2009 Google I/O developer
conference where Marcelo Camelo explains it all. See http://code.google.com/intl/sv-SE/events/io/2009/
sessions/PerformanceTipsGeoApiMashups.html.
Mapping Fundamentals
In the next chapter, you’ll get your hands dirty and start creating your very first map. But before you do
that, a basic understanding of how mapping works will make it easier to learn the API. Actually, you
don’t need to worry that much about how maps work since the Google Maps API takes care of most of it
for you. You do, however, need to understand how coordinates work.
Coordinates
Coordinates are used to express locations in the world. There are several different coordinate systems.
The one being used in Google Maps is the Word Geodetic System 84 (WGS 84), which is the same system
the Global Positioning System (GPS) uses. The coordinates are expressed using latitude and longitude.
You can think of these as the y and x values in a grid.
■ Note A source of confusion is the order the values are presented. Although the values in a grid are normally
presented with the x value first and the y value second, latitude and longitude do the opposite. They are presented
with the latitude value (the equivalent of y) first and the longitude value (the equivalent of x) second.
Latitude measures from south to north, and longitude measures from west to east. At the equator,
the latitude is 0. This means that everything below the equator (the south hemisphere) has a negative
number, and everything above it (the north hemisphere) has a positive number. Similarly, there’s a zero
line for the longitude too. It’s called the prime meridian, and for historical reasons it runs through
Greenwich, England. Every position that is located east of this line has a positive number, and everything
west has a negative number (Figure 1-2).
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