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Effective Cartography

Nuts and Bolts of Cartography with ArcGIS

An improved version of this tutorial is being maintained by the author at www.gismanual.com/mapping.

The goal of this tutorial is to provide hands-on experience with the techniques of producing context maps in ArcGIS. Transforming data into graphics that communicate key ideas about how our area of interest consists in a network of named physical and cultural features connected by corridors of various types and interrupted by edges, barriers and invisible boundaries. We assume an understanding of our first tutorial, Collecting GIS Data and Metadata in ArcMap.

Download the Tutorial Dataset

Background

Objectives of this Tutorial


Begin with a Purpose

Having a goal makes any endeavor interesting. All of the maps we make should have a specific, stated communication goal. It goes without saying that without this, a map is pointless and cannot be evaluated. In the case of this tutorial, we are carrying forward the goal that framed our first tutorial> We want to understand how the proposed extension of the MBTA Green Line will affect the city of Somerville, Massachusetts. This particular mapping project will examione the context of the neighborhood Union Square as it is today, as the setting for two of the proposed stations on the greenline extension.


Understand Map Projections

Our assignment is to make maps of regional and local context. On maps of this scale, we should assume that the assumptions of topographic interpretation will apply, namely:

You may take these assumptions for granted, as would most map users, however, we will see that assuring that these assumptions hold true requires acive attention to the choice of a map projection.

Start your Map by Opening a Layer

We will begin our map by going to our data collection and adding some information that we captured from ESRI streetmap according to the method described in Beginning a GIS Database. Here we will observe that arcmap sets the map projection of our Data Frame to adopt the native projection of the datasets that we open. To make this clear, we will begin by opening some world-wide reference layers that will help us choose an apropriate projection for our map.

  1. Start a new map document in ArcMap
  2. Inspect the Dataframe Properties (double click the thing called Layers at the top of the table of contents to check the geometric transformation being applied to the map.
  3. From the tutorial dataset, add the world_countries.shp shape file from the world_reference folder of our sample dataset.
  4. Check the coordinate system properties of the world_countries.shp layer -- listed among teh Source Proerties for the layer. See how the dataframe adopts the coordinate system of the first dataset that you open.
  5. Check the projection properties of the data frame. See how the data frame has adopted the coordinate system of the first layer we have opened.
  6. Add the layers from the streetmap folder within our greenline_ext folder. YOu will find this in /sources/esri_streetmap/roads.lyr, and check the spatial reference property of these datasets.
  7. add the USGS_Hydro, MBTA, towns and openspace Layers from the greenline_ext/sources/massGIS folder.
  8. Take a look at the native coordinate system of the MassGIS layers. Note that the ArcMap project is transforming the geometry of the massGIS data to overlay with the other layers, even though the data have their coordintaes defined according to two different systems!

This sequense of steps illustrates a couple of important things. First, that the projection of our map is determined by the order in which we add datasets to tne map. Second, that subsequent layers that have their coordinate systems defined can be transformed on-the-fly to overlay coherently with the other layers in the map, regardless coordinate systems inherent in the other layers.

Investigate the Geometric Properties of your Map

If you thought that our discussion of map projections in class was merely academic, the following series of steps should drive home the fact that a failure to understand the projection of a map can lead to a very major blunder. Understanding this, you will agree that a map intended to be used for interpreting shapes and directions should declare what projection has been used to transform the data.

References