GIS in Historical Research: The North-West Shropshire Tithe Maps and Apportionments

 

Introduction

Capturing the Data Digitally

The Entity-Relationship Diagram

Data Normalisation

The Database Table Structure

Working with the Database

 

Data Normalisation

Data normalisation creates a logical view of the data as it will be laid out in tables and map layers. As a first principle, there will be a table or map layer for each entity. In this case the land use areas is a map layer and the parish, tithe areas, land parcels and person entities are tables.

The attribute table for the land use areas has an identifier column, three columns for area (acres, rods and perches), and columns for description, land use, and township. The land parcel table has columns for the land parcel identifier and for the land use area identifier(s) that indicate which land use areas make up the land parcels.

The person table has the surname, christian names and titles of everyone mentioned in the apportionment. Each person is given a unique identifying number. A conservative principle is used in drawing up the table; the same name appearing twice in the apportionment is treated as a different person unless there is positive evidence that it is the same person. There are, for example, two Joseph Hignetts in Hordley Parish; the conservative principle maintains the distinction between them by assigning them separate identifiers.

The attribute table for the tithe area has columns for the tithe area identifier and for the land use area identifier(s) that indicate which land use areas make up the tithe areas. There are also columns for the amount of tithe payable and the name of the tithe collector. In this form there is more than one piece of data in some cells (repeating groups); a tithe area may have more than one tithe payable. A section of the table in un-normalised form is illustrated below. 

Tithe Area ID Land Use Area ID Tithe Amount Pounds Tithe Amount Shillings Tithe Amount Pence Tithe Collector
B215 123  

 

 2
 
3
10
10
7
Rector of Hordley
Vicar of Baschurch
David Martin
B216 124  

 

1
 
1
 
4
5
Rector of Hordley
Vicar of Baschurch
David Martin
B207    125    126  

 

 

 

2
4
Rector of Hordley
Vicar of Baschurch

To normalise the data the repeating groups must be removed by splitting the attribute table in two; a link table with the ID columns and a tithe table with a tithe area identifier column, tithe amount payable and tithe collector columns. Sections of the normalised tables are illustrated below.

Tithe Area ID Land Use Area ID
B215 123
B216 124
B207 125
B207 126

 

Tithe Area ID Tithe Collector Tithe Amount Pounds Tithe Amount Shillings Tithe Amount Pence
B215 Rector of Hordley   2 10
B215 Vicar of Baschurch     10
B215 David Martin   3 7
B216 Rector of Hordley   1  
B216 Vicar of Baschurch     4
B216 David Martin   1 5
B207 Rector of Hordley     2
B207 Vicar of Baschurch     4