| This section covers the three basic
map concepts you need to know to effectively create your own maps
of any area within Oregon using our collection of Geographic Information System (GIS) data layers. Please note, the layers shown on the map depend on the geographic area or theme of the portal.
Map Concept #1: Map and Attribute Information.
Think of a lake in Oregon. How would you keep track of and communicate
information about this lake to other people who need to know about it?
You might use a database to keep track of the name of the lake, the average depth
of the lake, water quality information, the type of lake, and any other attributes that are
important. This lake is one record in a database. We call
each category (i.e. average depth) a field.
Now imagine you need to keep track of every lake in Oregon, including its location. Because you are now dealing with more than one lake, you will have multiple records in the database (one for each lake).
As you map the location of each lake and identify its attributes, you are building the foundation of your GIS data layer. You will be able to examine the attributes of lakes, rivers, etc. as you navigate
Oregon Explorer maps.
Map Concept #2: Information is separated into layers.
 You can also have other layers of
information in your map. Your information on lakes would be one
layer of information. You could also have a layer with rivers and a layer
with pine trees. Any information can be represented as a layer.
 With individual layers you can conduct analysis
between layers and only display layers of interest.
As you work with Oregon Explorer maps you will be able to turn
different layers on and off as you desire.
Map Concept #3: Map Scale
What is scale? Scale represents the ratio of a distance on the map to the actual distance on the ground.
When you zoom in on an online map, the scale of the map increases (it gets larger).
Maps are often known as large-scale or small-scale. A large-scale map covers a smaller land area than a small-scale map. A map that
is zoomed in to a small town is large scale, while a map of the United States is small scale.
For example, a map scale of 1:50,000, tells us that 1 unit of measure represents 50,000 of the same units on the earth's surface. Therefore 1 cm on the map represents 50,000 cm on the ground and 2 cm represents 100,000 cm. We can then calculate that 2 cm on a 1:50,000 scale map would equal 1 km.
Oregon Explorer maps have limits on the scales at which you can view the data. For example any layer with a red asterisk cannot
be viewed at the current scale. You must zoom in to be able to see that layer. As well, some map labels
may only appear at certain scales.
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Tutorial
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