Geography Reference
In-Depth Information
Manual Data Loading
While the name of this type of input may suggest the same as external data, the actual data
obtained in this step is usually very different. Data coming into the system via this input will
often be in the form of pre-provided data from a GIS data provider. In the United Kingdom,
this will often mean data provided by companies like Ordnance Survey. In the United States,
this might mean data provided by institutions such as the U.S. Geological Survey or TIGER
data from the U.S. Census Bureau.
At this step, wherever data is obtained from, it's almost guaranteed that it will need to be
transformed into a format that is useable in the GIS it's destined for. More often than not, it
will need to go through some kind of in-place process before it's useable in any way.
Regular SQL Queries
Since most GIS have a large database at the center of them, SQL still plays an important
role and probably always will. However, in GIS terms, these queries not only involve the
normal SQL that you're used to seeing in a database management system, but also
geospatial SQL. We'll cover GIS-specific SQL a little later on; for now, inputs here are
usually generated from things like search queries.
As an example, when you type the name of a place or a ZIP code into Google, Bing, or
Yahoo Maps, the web application you're looking at will most likely turn your search into a
query that uses geospatial SQL to examine data in the core database. This, in turn, will be
combined with other processes to produce an output, which in this case will usually be a
map displaying the location you searched for. Another example might be an operator in an
emergency services control room entering the location of an incident, and combining that
with the known locations of nearby emergency vehicles to aid in making a decision as to
which vehicle to send to the incident.
Location-Aware Inputs
The last input type is probably the one that is familiar to most people. Location-aware data
most often comes from the GPS input on a mobile phone or other GPS-enabled device. It is
generally common latitude and longitude information. We'll cover this more when discussing
NMEA data.
Graphical Outputs
Now we move to the output layers, the first of which is the graphical one and what most
people are familiar with. Output data here is very often in the form of a raster-based map
with all operations performed to produce a single output tile in the form of a standard bitmap
(such as a .jpeg). However, far more is involved than simple map tiles. Graphical outputs
can, and very often are, produced in various vector formats, or as things like AutoCAD
drawings for loading into a CAD or modeling package. In fact, even in web environments
where people are used to seeing bitmap tiles, it's common for graphical output to take the
