Technical Notes: Thematic/Choropleth Map with ArcGIS

Introduction: With Geographic Information System (GIS) we can visualize and analyze spatial data. Any data that includes information about location - be it a street address, zip code, longitude, latitude or X/Y coordinates - can be considered as spatial data. Here I’ll create a very simple thematic/Choropleth map with ArcGIS ArcMap 10.2. Trial version of ArcGIS for desktop can be downloaded from this location- http://www.esri.com/software/arcgis/arcgis-for-desktop/free-trial.

Steps:

Start Program-> ArcGIS-ArcMap 10.2 – then open an new empty map.

Click the “plus”

sign on the standard toolbar to add Data. Alternatively we can add data from File menu and then selecting Add dat. When the “Add Dialog box” appears, navigate to the folder where data file/shape file is stored. We can also click on “Connect To Folder” (

) and navigate to data file. I have downloaded 2010 USA Population data (State_2010Census_DP1.zip) from http://www.census.gov website and unzipped the files at c:\zip\CensusData\State2010Census.

After adding “State-2010Census_DB1.shp” file, it’ll appear as USA map with state boundaries as follows:

We can use Pan,Zoom-in, zoom-out

tools to move around the map. Data layer (state_2010census_DB1) is visible on table content pane. Right click on data layer and then select “open Attribute Table” to see the fields in this dataset. Here is how the table looks like:

We are interested in two fields - DP0010001 (total Population ) and DP0160001 (Avg. Household Size).

Let’s change the field name - Right click on data layer->properties->fields and then select DP0010001 and change alias as ‘Total Population’. We’ll do the same for DP0160001 to name it ‘Avg. Household Size’.

Now we’ll use the field- ‘Total Population’ and make it a Choropleth map. Let’s open Layer property page by Right clicking on data layer->Properties->Symbology. On Symbology tab select ‘Total Population’ field from value dropdown and select 7 from classes drop down. Select Color Ramp of your choice. It should look like as screen below:

To format the labels, click on label > format Labels -> Number Format-> highlight Numeric and check “Show Thousands Separator” Hit OK.

To display USA State Name, Right click on data later->properties->Labels and then select “STUSPS10” from Label Field drop down and press apply. Again right click on data layer and then choose “Label Features”.

The map should look like this :

Now let’s add another layer for Household Size. Copy data layer (state_2010Census_DP1) and paste it on Layers. You’ll see two data layers (state_2010Census_DP1) under layers. To display “Avg. Household Size” data, right click on new data layer- and navigate to properties->symbology. On symbology tab select “Dot density” under quantities and select “Avg. Household Size” under field selection.

It shows 1 dot is equivalent to 0.1. To add this layer on top of population layer that we built earlier, we need to make this layer transparent. To do this, right click on new data layer and then properties and then display – change “transparent” to 70%.