In today's lesson, we'll add a layer to your map. What is a layer? A layer can be thought of as a container for geographic data that is alike – for example, you might have a layer containing roads, another containing rivers and still another containing cities. Your map can contain as many different layers as you like, and you can manipulate them individually to achieve the appearance that you want.

Layers are different from the base maps that we discussed in the previous lesson. Whereas base maps are backdrops that can't be styled, queried or transformed, most layers can be greatly manipulated to achieve a particular appearance or to adhere to a specific set of criteria. With layers, you can apply specific styles, change shape geometries, run queries, perform geoprocesses and much more.

There are two main types of layers: vector layers and raster layers. In today's lesson we will be adding a vector layer to your map. What is the difference between these two types? Let's explore:

• Vector layers consist of a series of points that use math to connect the dots and fill in the shapes or lines created by those points. The points used in vector layers are similar to those of a graph: they use (x,y) coordinates, and these coordinates are drawn on your map as polygons, lines, or points. Because of this simplicity, vector layers produce a small file size compared to raster layers. Examples of vector layers include:
  • Interstates/roads
  • Restaurant locations
  • State boundaries

• Raster layers use pixels instead of coordinates to create their data. These layers are extremely detailed and can show mass amounts of information. Each pixel can be assigned a specific value, and are used for a more continuous type of data. However, the file size of a raster layer can be quite large, and it is difficult to edit this type of layer. Examples of when raster layers are useful include:
  • Aerial photographic imagery
  • Rainfall amounts
  • Soil PH
  • Salinity of a water body

Let's start by opening the GIS Editor project we created in Lesson 1, “Creating Your First Map”. To open your project in the GIS Editor, click on the dark blue button in the upper left corner of the application window. This will open the Main Menu. Select the option that says “Open Project”. Then navigate to where you saved your project and double-click its name to open it.

After opening our project we can begin to add layers. In today's lesson we will add two vector layers to our map: “USStates”, which contains all the states of the United States, and “USInterstateHighways”, which contains lines representing the major U.S. interstate highways. But where do we find these layers? Recall from our last lesson how useful it is to store all of your map data in the GIS Editor's Data Repository. The Data Repository is where we will find the data files for our layers, as well as several other sample layers that come included with the GIS Editor.

The Data Repository lets you store all of your different layer data files, CSV files and base maps, no matter where they reside on your computer or your network. This eliminates wasted time trying to locate all of your different data files. The repository is great for aggregating sets of disparate data in a single place so that they can be accessed very quickly.

If you don't already see the Data Repository window, click the “Open Data Repository” button on the Home tab of the application's ribbon bar. Now that we have our repository open, we can easily add both the “USStates” and the “USInterstateHighways” layers onto our map. In the left side pane of the Data Repository you should see an entry for “Data Folders”, and underneath that, another entry for “Data”. Select the “Data” entry to see what layers are inside it. Your screen should now look like this:

In the right side pane of the repository you should now see several different sample layers that come with the GIS Editor. All of these sample layers are in a format called Shapefile, which is an industry-standard vector data format that can contain polygons, lines, or points (but never a combination of the three). To add any of the layers shown here to your map, simple double-click on it. As stated earlier we will be using the “USStates” and “USInterstateHighways” layers, so let's start by double-clicking on the “USStates.shp” item now.

When you double-click the item, the Style Wizard window will appear. This window walks you through the process of applying a custom appearance to the layer you just added. For simplicity, for now just click the Cancel button to close the Style Wizard and accept the default appearance for the layer. We will talk more about the Style Wizard in an upcoming lesson.

You should now see that the “USStates” layer we just added is displayed on your map, and that there is also an entry for it on the left hand side of the GIS Editor window under the Layer List heading. Next, go ahead and add the “USInterstateHighways” layer as well. You should now have two layers in your Layer List, and you should see the highway lines snaking across the states on your map.

Let's discuss the Layer List for a moment. The Layer List shows you all of the layers that are currently on your map and allows you to manipulate and reorder them. Changing the layer order is especially important because it dictates the order in which each layer will be drawn on the map. Layers that appear higher in the Layer List will draw on top of layers that are listed below them. For example, if your “USStates” layer was listed above the “USInterstateHighways” layer in your Layer List, the states would cover up the highways and the highways would therefore be invisible on the map.

To see how this would look, try clicking and dragging the “USInterstateHighways” layer so that it is underneath the “USStates” layer. You should see the roads on your map disappear. This is because they are actually underneath the states. Now go ahead and drag the highways layer back up to the top of the Layer List, and the roads should reappear.

The Layer List also provides a convenient way for you to quickly hide and unhide any layer. To hide the highways temporarily, uncheck the checkbox on the left side of its box in the Layer List. Whenever a layer is unchecked in this fashion, it will disappear from your map. You may need to do this occasionally when you are building complex maps, in order to see the details of a particular layer without other layers getting in your way.

Congratulations on adding your first two layers to your map! Now that you have finished, let's save our project for use with the next lesson. To save your project, simply click the “Save Project” button on the Home tab of the ribbon bar, or click the small blue diskette icon in the top left corner of the screen.

In the next lesson, we'll learn about importing in your own custom data into the GIS Editor and associating it with the geographic data on your map. Head over to Lesson 3 to get started.

Continue to:
Merging In Your Own Custom Data

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