riverPolys_winterriverPolys_spring

These images were created using ArcGIS. Not everything is tables, geographical coordinate systems and tool operations. These winter and spring colored images derive from one vegetation raster on the Tanana River area south west of Fairabanks, Alaska.

This short step by step guide will demonstrate how to create images like the ones above. In order to get started you’ll need a copy of ArcGIS and a source raster. You may download veg.zip. It contains the raster veg.img and the meta data for the raster in veg.img.xml. The original raster comes from a GIS analysis class I took at the University of Alaska Fairbanks, NRM 341 in the Spring of 2009. The source raster was labeled veg.img. It’s meta data is veg.img.xml.

I used a student licensed copy of ArcGIS 9.3 that was distributed during the semester.

First, create a new map and insert the veg.img into your ArcMap document. You should see something like this:

The veg.img file loaded into ArcMap

The veg.img file loaded into ArcMap

Now make sure that you have your spatial analyst extension enabled and locate the Raster to Polygon (conversion) tool. You can quickly find any tool by clicking on the Index tab of the toolbox window and typing the first few letters of the tool.

Toolbox showing the Index tab and quick search to the Raster to Polygon tool

Toolbox showing the Index tab and quick search to the Raster to Polygon tool

Open the tool and you will see something like this:

Raster To Poly Tool operating on veg.img

Raster To Poly Tool operating on veg.img

Once the tool executes you will get an image like the one below. Your initial color for the image may be different than this:

Raster to Polygon Tool Result

Raster to Polygon Tool Result

At this point you can remove the veg.img from your document or just hide it. This tool has created polygons for each of the raster zones in veg.img. The image tanana_vegetationPolys has a unique number for each polygon in its bounds. We will change the properties of tanana_vegetationPolys so that a different color is used for each number. Go ahead and right click on the tanana_vegetationPolys and select Properties….

You’ll see a new window called “Layer Properties” with many tabs. Select the “Symbology” tab to get something similar to this:

The Layer Properties / Symbology Tab showing display properties for our polygon image

The Layer Properties / Symbology Tab showing display properties for our polygon image

Now the trick here is to select a color scheme that is pleasing to your eye. The colors shown in the image immediately above reflect a fall theme. If you’d like something different select the drop down menu under the “Color Ramp” section and make another choice. I selected a greenish summer theme as shown below:

My initial green color scheme

My initial green color scheme

You can see all 711 or so polygons with its color rectangle under the tanana_vegetationPolys polygon theme. While you can make out the shape of the sweeping Tanana river, its nice to make it really stand out with a nice shade of blue. A really easy way to figure out the polygon ID for the Tanana river polygon is to use the identify tool:

The identify tool selected

The identify tool selected

Go ahead and click on the river with the identify tool and you’ll get a window similar to this:

The river polygon identified

The river polygon identified

Notice that the GRIDCODE field reads 88 and the ID field reads 698. The GRIDCODE was the value the river pixels had when they were in the raster. This information has been carried over to the current polygon, but its not what is helpful now. Right now you’ll want to grab the ID field being 698 and scroll down to that color rectangle in the expanded layers section of your ArcMap document. Double click it and change the color to a blue:
blueSymbol

change the 698 ID polygon to blue

change the 698 ID polygon to blue

You may wish to further manually select certain polygons and change the colors into something that would best represent a gravel bar, bank sand, etc. Once you are satisfied you’ll want to save your image. Make sure first you save your ArcMap document, you can always come back later and use different rasters, color schemes or parts of your document over again. But for now you’ll want to export the image:

Exporting the Map

Exporting the Map

Done!