A Density Map visualization is useful for quickly grasping patterns and trends for a large number of geographic locations. It allows to display the data on an interactive map as areas color-coded based on the population density of locations on the map. It is usually done by mapping the density values to a grey or color scale. This lab is going to create a density map visualization of New York public schools on an interactive map.
The data of the public school locations is acquired from the NYC open data website. The data is provided by the Department of Education, 1,709 school are included and the data is updated on September 2017. The data is an ESRI shapefile of school point locations based on the official address and includes some additional basic and pertinent information needed to link to other data sources. It also includes some basic school information such as Name, Address, Principal, and Principal’s contact information.
The dataset is downloaded as .zip file, and is imported to the Carto web browser. The data is then viewed in Carto to check if further cleaning of the data is necessary. The data include the necessary geospatial dimension and no further cleaning of data is necessary. The dataset is ready to use and is opened as map. The layer is renamed as Public School for clarification. A Dot Map is created where each dot represents one school.
A Dot Map of public schools is created where each dot represents one school.
A data of Boundaries of Neighborhood Tabulation Areas of NYC is also downloaded from the NYC open data website for creating a density map of public schools of each neighborhood. This data is created by the NYC Department of City Planning using whole census tracts from the 2010 Census as building blocks. The data is imported to the Carto website and is added as a layer to the public school map. The layer is renamed as NYC Neighborhood.
To show the density of public schools of each neighborhood in New York City, the data of Public School has to integrate with the data of NYC Neighborhood. This is done by applying the Intersect and Aggregate analysis option to count the number of points that intersect in each neighborhood.
To indicate the density of school in each neighborhood, a sequential color schemes is used to represent the relationship and quantitative differences. An example of a density map from Mapping Indiana’s Public District School Choice Transfers is used as a reference. In this map, the lower data value is represented by a lighter color, and a higher values is represented by a darker color.
Mapping Indiana’s Public District School Choice Transfers from edChoice
In our map, the points is displayed as a value of color, and a sequential color schemes is created where the higher density is associated with darker purple, and the lower density with a lighter purple. A white stroke is used to separate the neighborhood. No labels are used to indicate the number of points on the map as the colors already indicate the density. A color scale is used to indicate the color value. Pop-up icon is created to show the detail information about the number of school in each neighborhood. In order to increase of the contrast, a positron style map is used as the based map so that the base map will have a monotone color and will not disturb the color of the density map.
Density Map of New York public schools. The higher density is associated with darker purple, and the lower density with a lighter purple.
I would also like to include the five Boroughs of New York City. The data of the borough boundaries is acquired from the NYC Open Data. The data is then uploaded to the Carto website and is imported as a layer to the map. The layer is renamed as Borough Boundary. If different colors are used to indicate the boroughs such as the one from the Wikipedia website, it will create too much disturbance to the map.
Map of New York City boroughs. Different color is used to indicate different boroughs.
Since the boroughs are not our main focus in this map, I want to use the boroughs as a reference only and do not want to interfere the density map. Therefore, a monotone with a similar but a darker color of the base map is chosen as the outline of the boroughs.
A monotone with a similar but a darker color of the base map is chosen as the outline of the boroughs.
It might be more interesting to show both Dot Map and Density Map at the same time. An example can be found in the Heat Map in the GIS Lounge website. A color gradient is used to indicate areas of increasingly higher density, and at the same time, the point density is displayed in the map.
Heat Map in the GIS Lounge website. A color gradient is used to indicate areas of increasingly higher density and the point density is displayed in the map as well.
Since it will be overcrowded if the Dot Map and Density Map are both displayed at the same time. Therefore, a Layer Selector is used to allow the selection of different layers. In our map, in order to increase the contrast between the points and the polygon, a green color with white stroke is used to indicate the points of the school. The density map is show as follow:
In the future, if I am going to create a data map that is gender oriented, I would test the color in the Color Blindness Simulator so that I will have a more clear understanding of how the colors will look like in a color vision handicap.