Now you are going to begin digitizing features of this image. Digitzing is the process of making features we can see on the Manhattan image editable and making them features to which additional spatial and non-spatial attributes can be assigned. This means we are going to follow a process of making digital versions of objects that will have an attribute table associated with them. Our primary goal will be digitizing the Wards, which are objects that occupy an area on the map, once they are digitized and have an associated attribute table these objects will also be known as polygon features. In an accompanying document you have data on the home country of Mothers by Ward. When digitizing we can digitize points, lines, or polygons. By digitizing these features, you make them available for mapping once you have added the tabular data to the attribute table (as you know there are a few ways you can do this). The digitizing process is started by creating new layers in ArcCatalog, and then adding features to them in ArcMap.
Creating an empty shapefile. Open ArcCatalog. We are going to create a new shapefile that we can edit in ArcMap—this will be a polygon feature shapefile to which we will add ward boundaries. In ArcCatalog, browse to the location of your current mxd file. This is the folder in which you will create your new shapefile, so select that folder and right-click on it. Go to New Shapefile… to open the Create New Shapefile window. Give the polygon shapefile an appropriate name such as ManhattanWard. Click on Edit… to see the Coordinate System of the file. In the Spatial
Reference Properties window click Import… to use the projection of the manhattan street layer. Click OK and OK again to create the shapefile.
Add a new filed in the Attribute Table. Return to ArcMap, and add your new shapefile to the Data Frame (TOC). If you open the Attribute Tables of this shapefile you will find it empty. We are going to use this empty shapefile to create features from our image.
Now you will start working with the new shapefile. Before you start editing, first open its Attribute Table. Click on the Options button and Add Field… First create a Short Integer (choose in the Type drop-down menu) field called Wards where the Ward number identifier will be entered. Note that you cannot create new fields while you are editing a layer.
Digitizing Wards and entering tabular data. You will need the Editor toolbar. View Toolbars Editor. On the toolbar, click on the Editor menu and Start Editing. You will be prompted to choose the folder that your shapefiles are in, and then click OK. Before you get started creating polygons, turn off all but the registered manhattan image layer.
In the Editor toolbar, Start Editing. Choose MahanttanWard (or whatever you named it) layer as the layer you want to edit. In the Editor toolbar, Create New Feature. You are going to create a polygon for individual wards, it is probably easiest to start with some rectangular shapes. There are some good ones south of central park. From the pull down menu next to the Editor pull down choose the sketch tool.
By clicking at the four corners (single clicks) of the ward you are digitizing you will create a continuous outline of it. Double clicking when you get back to where you started will finish your Sketch. This should make your polygon become an actual, filled polygon. If you make a mistake you can select and delete sketch. You can digitize 3-5 ward boundaries and enter corresponding ward ID numbers into the Wards field in the attribute table.
Extension Activity
Now that you have digitized a few polygons in ArcGIS you have acquired the skills to create editable features from scanned maps that can be linked with tabular data. If you are interested you can do a number of things to extend what you have learned. You can digitize the rest of the wards, create new fields in the attribute table, and either edit or link the 1890 Ward data in order to create a map of 1890 demographic patterns for Manhattan. You can also do just a subset of this work and map a few wards and link or add the data to create a map of 1890 demographic patterns. What you are doing has not been done before, you will be creating some of the first digital maps of Manhattan in 1890, have fun!!
