How to generate Buildings ID numbers inside parcels

Question

In order to decrease manual data entry, I would like to automate a task to generate numbers for all buildings inside a parcel starting with 1. For example, I have 4000 parcels and each parcel has many buildings. An example of what I would like to achieve is shown in this diagram:

Answer 1

If you're looking for an ArcGIS solution and you have a bldg footprint polygon layer as your pic indicates, then it may be relatively straightforward to:

1- Perform a spatial join, parcels (source) to bldgs (target) so that your bldgs layer will 'inherit' the parcel IDs of your parcel layer.

2- Add a new numeric field for which to calculate the bld nos.

3- Run the following script which opens an update cursor on the output spatial join fc based on a sort of the parcel ID field. The script is untested, errors are not trapped - comments are included in the code, so modification as required should be easy.

import arcpy

# ---set a few variables in-between the 2 symbols: <> 
# (remove the symbols, no spaces or special char between the quotes)

# your workspace:
arcpy.env.workspace = r'< your workspace pathname >'
# your output fc from the spatial join:
fc = '< your spatial join output fc name >'
# your fieldname for parcel ID:
parcelID = '< parcel id fieldname >'
# your new fieldname for housing the newly assigned bldg number:
bldgNO = '< bldg number fieldname >'

# STOP - no more variables to assign

# the following var is for providing the sort string in UpdateCursor
sort = parcelID + " A"
# create the update cursor object
cursor = arcpy.UpdateCursor(fc, '', '', '', sort)

# initialize counter 'i' and current value 'currentVal' for parcel ID
i = 0
currentVal = ''

# process each row represented by 'bldg'
for bldg in cursor:
    # successive parcelID equiv to currentVal, bldg i
    if bldg.getValue(parcelID) == currentVal:
        bldgNumber = i
        # set the bldg val in the table
        bldg.setValue(bldgNO, bldgNumber)
        # update row object
        cursor.updateRow(bldg) 
        # increment i
        i += 1
    else:
        # re-init i (currentVal is '' for 1st row, otherwise not equiv to parcel ID)
        i = 1
        # set the bldg val to 1 in the table
        bldg.setValue(bldgNO, i)
        # update row object
        cursor.updateRow(bldg) 
        # set currentVal to the current parcel ID used for next row val comparison
        currentVal = bldg.getValue(parcelID)
        i += 1

# finally, del objects to remove locks on data
del bldg
del cursor

Answer 2

you can use QGIS for this operation. Given below is simple steps which is easy for any level of users.

• Open data in QGIS.
• Right Click on Layer name and choose "Toggle Editing".
• Right Click again and Open Attribute Table.
• Open Field Calculator (Ctrl + I).
• select "create new field" and say a field name.
• Expand Record and choose rownum (double click). click ok and it will generate numbers for each record in attribute table.

Open Attribute Table to verify your results

See the screenshots below