Assessing What We Have and What We Need to Solve the Problem
What we are going to do is find the census Blocks polygons that lie within three miles of Galbraith School Road. But since our objective is to find population we have to first join the census table to the Blocks table, so that the number of people in each census block will be available to us. To join these two tables, we need to find a key field in each table whose values serve as block identifiers. In the census table that key field is GEO_ID_L4D. In the Blocks table the key field is BLOCK2000.
____ 23. Look at the attribute table of Blocks. In the column BLOCK2000 we have the four-digit block number. In the Layer Properties window check out Fields. Note that BLOCK2000 is a String field of Length 4.
Look at the table Census4. In the GEO_ID_L4D column you see four-digit block numbers. In the Layer Properties window check out Fields. Note that GEO_ID_L4D is a String field of Length ________. (We will hope that it will match up with BLOCK2000 string field of length 4 when we join the tables.) Also note that we have P001001 which is the population of each block. Dismiss both tables.
Next we need to join the Blocks table and the Census4 table so we can combine the geographic information of the shapefile with the tabular information in the census file.
____ 25. Right-click Blocks and choose Joins and Relates > Join. Under “What do you want to join to this layer?” choose “Join attributes from a table.” For Step ...