Class is in...

When I started this blog several years ago, the original intent was to provide notes for a sales team and clients.  It was a basic cartographic education for people who have no background in displaying data on maps, or who would simply hit defaults in the software they are using with little thought to what they are describing.  The goal was to provide enough information so they may make better decisions not just in the map making process, but in interpreting maps as well.

Choropleth

One of the most common maps you may see, especially in the media, is a choropleth or shaded area map.  The goal is to compress vast amounts of data into digestible portions for the map readers. Whereas a table of numbers provides details for individual locations, the map should generalize these locations; collecting locations together into chunks of similar values making the map easier to interpret. These chunks are called classes.  The process of chunking is referred to as classification.

Grid Systems, a brief introduction

Let there be grids

Outside of ZIP codes, there are other methods we like to utilize to map our data. One of these is the use of a grid of some arbitrary size over a large area. Many types of data can be mapped to a grid. Temperature, precipitation, elevation each lends themselves to grids due to their continuous nature over a surface. Sometimes other types of data are projected onto grids that are not necessarily continuous, population, geologic formations and income for instance. Grids are also useful for simply indicating locations of geographic features, and have most often been exploited historically for that purpose.

Mapping with Mr. ZIP

ZIP code areas and what they can (and can't) do for you

I am often requested to map or facilitate the mapping of some data by ZIP code. The desired result is a thematic choropleth (or heat map) of sales/customer data for these ZIP code divisions . The request itself is not unreasonable, but filled with difficulties inherit to the nature and history of the US ZIP code system.

The problems mapping data by ZIP code areas ultimately originate with the idea that we live in a ZIP code. The very idea of a ZIP code area is ingrained in our minds as these static geographic units with definite boundaries that divide people into manageable groups-this concept even creeps in from pop-culture, ala Beverly Hills, 90210.