Working with Vector Data - Desktop GIS: Mapping the Planet with Open Source Tools - page 51

The X and Y of Latitude and Longitude
In conversation, most people say “latitude and longitude,” not
the other way around. In fact, you will most often see it written
that way as well. So, it's natural for people to assume the lati-
tude = X and longitude = Y (since we say X,Y), but this isn't so.
It's an extremely common mistake, especially for newcomers
to the GIS realm. For the record, lines of longitude run vertically
and measure units in the X direction. Lines of latitude run hori-
zontally and measure units in the Y direction.
The output can be used for importing into another application for
further manipulation or reporting purposes. You might be wondering
about the funny-looking POINT notation. It's the Well-Known Text
(WKT) representation of a point, consisting of the feature type keyword,
in this case POINT, and the coordinates (X and Y) separated by a space.
The X and Y values are in the coordinate system of the layer. In the case
of our cities layer, it's geographic (longitude, latitude). We also have the
name, the country, its population, and whether the city is a capital.
Advanced Search
The attribute table also provides an advanced search query capabil-
ity where you can really narrow down what you are looking for in the
dataset. The quick-search feature allows us to specify only a single
search term and field to search. With the advanced query, we can be
more specific by using SQL. 8 Don't worry if you aren't a SQL expert or
don't even know what it stands for—QGIS makes it easy, as we will see.
Say, for example, we want to find all the cities in the world with more
than 2 million people that are also capital cities. We can easily do this
with the Search Query Builder. To access the builder, open the attribute
table, and click the Advanced button. The query builder populated with
the terms needed to find the cities of interest is shown in Figure 3.19 ,
on the following page. Now let's take a look at how this dialog box works.
The fields in the attribute table are listed on the left side of the dialog
box. On the right is a box that can be used to display the values for a
field. This allows you to get a preview of a field's contents to aid you in
building the query.