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Chapter 5 Working With Digital Spatial Data and GIS
real-world information. For instance, if you were tasked to make a map of all
of the stop signs in your city, you’d need to be able to represent the locations
of all the signs on a map at the scale of the entire city. By laying out a map of
the city and placing a dot at each sign location, you would have a good representation of them. The same holds true if you had to come up with a map of
all the roads in your town. You could attempt to draw the roads at their correct
width, or more likely, just drawing a line along the road’s path would suffice
for representing the road locations.
Whenever you’re deciding how to model real-world phenomena with a
GIS, you first have to decide on the nature of the items you’re trying to represent. When trying to represent the real world in the GIS, there are two ways of
viewing the world. The first is called the discrete object view. Under this way
of thinking, the world is made up of a series of objects that have a fixed location,
or a fixed starting and stopping point, or some sort of fixed boundary. A street
starts at one point and ends at another, or there is a definite property boundary
between your property and your neighbor’s. Around a university campus, there
will be numerous objects—buildings, parking lots, stop signs, benches, roads,
trees, and sidewalks. By viewing the world in this way, real-world items can be
modeled in the GIS as a series of objects (such as a collection of lines to represent roads or a series of points to represent fire hydrant locations).
When adapting the discrete object view of the world to a data model, items
in the real world are represented in the GIS by one of three objects (Figure 5.2):
a Points: These are zero-dimensional objects, a simple set of coordinate
locations.
a Lines: These are one-dimensional objects, created from connecting starting
and ending points (and any points in between that give the line its shape).
a Polygons: These are two-dimensional objects that form an area from a
set of lines (or having an area defined by a line forming a boundary).
There are a lot of GIS applications available online
that are used for mapping and analysis of spatial
data. For some interactive examples, open your
Web browser and go to http://www.arcgis.com/
home (this is the Website for ArcGIS Online). We’ll
discuss a lot more about ArcGIS (and its manufacturer, Esri) later in this chapter, but for now, we’ll
be examining some of the online applications that
have been developed with ArcGIS. From the main
page, select the option for View the Gallery. Open
and examine some of the maps that people have
developed and posted online. When opening a map
application, you’ll be placed into a GIS environment
where you can pan around the map, zoom in and
out, and use an “identify” tool to get information
back about layers on the map. You can also select
the option for Make a Map, and a new Web page
will open where you can select an area of interest
(for instance, your state or county), then add data
from ArcGIS Online or select a new basemap to use
(including street maps, topographic maps, or highresolution imagery).
Hands-on Application 5.2
ArcGIS Online
discrete object view
the conceptualization
of the world that
all items can be
represented with a
series of objects.
points zero-dimensional
vector objects.
lines one-dimensional
vector objects.
polygons twodimensional vector
objects.
Chapter 5 Working With Digital Spatial Data and GIS
real-world information. For instance, if you were tasked to make a map of all
of the stop signs in your city, you’d need to be able to represent the locations
of all the signs on a map at the scale of the entire city. By laying out a map of
the city and placing a dot at each sign location, you would have a good representation of them. The same holds true if you had to come up with a map of
all the roads in your town. You could attempt to draw the roads at their correct
width, or more likely, just drawing a line along the road’s path would suffice
for representing the road locations.
Whenever you’re deciding how to model real-world phenomena with a
GIS, you first have to decide on the nature of the items you’re trying to represent. When trying to represent the real world in the GIS, there are two ways of
viewing the world. The first is called the discrete object view. Under this way
of thinking, the world is made up of a series of objects that have a fixed location,
or a fixed starting and stopping point, or some sort of fixed boundary. A street
starts at one point and ends at another, or there is a definite property boundary
between your property and your neighbor’s. Around a university campus, there
will be numerous objects—buildings, parking lots, stop signs, benches, roads,
trees, and sidewalks. By viewing the world in this way, real-world items can be
modeled in the GIS as a series of objects (such as a collection of lines to represent roads or a series of points to represent fire hydrant locations).
When adapting the discrete object view of the world to a data model, items
in the real world are represented in the GIS by one of three objects (Figure 5.2):
a Points: These are zero-dimensional objects, a simple set of coordinate
locations.
a Lines: These are one-dimensional objects, created from connecting starting
and ending points (and any points in between that give the line its shape).
a Polygons: These are two-dimensional objects that form an area from a
set of lines (or having an area defined by a line forming a boundary).
There are a lot of GIS applications available online
that are used for mapping and analysis of spatial
data. For some interactive examples, open your
Web browser and go to http://www.arcgis.com/
home (this is the Website for ArcGIS Online). We’ll
discuss a lot more about ArcGIS (and its manufacturer, Esri) later in this chapter, but for now, we’ll
be examining some of the online applications that
have been developed with ArcGIS. From the main
page, select the option for View the Gallery. Open
and examine some of the maps that people have
developed and posted online. When opening a map
application, you’ll be placed into a GIS environment
where you can pan around the map, zoom in and
out, and use an “identify” tool to get information
back about layers on the map. You can also select
the option for Make a Map, and a new Web page
will open where you can select an area of interest
(for instance, your state or county), then add data
from ArcGIS Online or select a new basemap to use
(including street maps, topographic maps, or highresolution imagery).
Hands-on Application 5.2
ArcGIS Online
discrete object view
the conceptualization
of the world that
all items can be
represented with a
series of objects.
points zero-dimensional
vector objects.
lines one-dimensional
vector objects.
polygons twodimensional vector
objects.