Interpreting Mapped Results

This map shows the results of the search you defined on the data search page, either as Pins or Polygons depending on the selections you made. You can manipulate the results at this stage in a number of different ways. Before drawing any conclusions from your results, you should read the important Health Warning at the bottom of this page.

Choosing a Base Map

In the upper right hand corner of the map you will find a pull down menu. The default setting is 1746. Leaving this unchanged will result in your data being mapped on to John Rocque's map of London of that date. But you can choose from five different alternatives:

  • 1746: John Rocque's map of London. Go to Background information on this map.
  • 1869-80: This selection will display your results over the first Ordnance Survey map considered fully geographically accurate - that first published between 1871 and 1880. Background information on this map. As the data available for mapping derives from the period before 1819, using this base map runs the danger of misrepresenting the urban character of the areas involved, but fully and accurately reflects the underlying geography of the region. Many of the borders used in defining parishes and wards were also taken from this late nineteenth-century map.
  • Blank:Using a Blank map will highlight the relationship between different elements of data, and is particularly useful for viewing the colour shading of polygons when you wish to explore the spatial distribution of events or information.
  • Map: This selection allows you to display your data over a modern schematic map of Greater London, derived from Google Maps.
  • Satellite: This will display your data over a photographic satellite image of modern London drawn from Google Earth.

The normal mouse commands for Google Maps and Google Earth work with this site; so you can zoom in using the icon in the upper left hand corner of the map, or by using your mouse wheel. You can also drag the map by left-clicking your mouse.

Data Boxes

Every time you use a Data search form to select new data, a new box will appear on the map page, displaying the data you have selected. The tick box in the upper left hand corner of the Data Box allows you to toggle on and off that particular set of data. The colour key for that data set is displayed in the upper right hand corner. The pull-down menu in the Data Box allows you to decide how to display your results - as, for instance, pins or polygons. See Display As below, for further details on this function. Directly below the Data Box, Add Data allows you to select an additional dataset to display on your map. There is no functional limit to the number of datasets you can map in this way. Reset view returns the map to the default scale.

Display As

In the Data Box you will find a pull-down menu that allows you to select how you wish to Display your results. The most appropriate display format depends on the nature of the data you have selected. The pull-down menu includes the following choices:

  • Polygons: A polygon is simply a bounded shape such as a square or triangle. In this context polygons can be parishes, wards, or other types of place such streets. The polygons dispayed on the map are determined by how you grouped your results on the data search form. For instance, if you grouped by Parish, polygons representing the parishes of London will be displayed on your map.
  • Polygons (no border): As with a simple polygon this display format divides your data between defined areas, but does not mark out their borders. This is particularly useful when exploring the distribution of densities (of crime or population for example) across space, and should normally be used with a blank base map.
  • Pins (per hit): This will display each hit as an individual pin. This is particularly useful when mapping a relatively small number of hits (under approximately 500).
  • Pins (grouped): This will display your hits as pins, but collect them according to type of place you have grouped by (such as parish), with the number of hits reflected in the size of the pin displayed. So, for instance, if there are 20 hits for 'St Dionis Backchurch' and two hits for 'St Botolph Aldgate', the pin for the St Dionis will appear substantially larger. This format is useful when displaying larger amounts of data.
  • Polygons Adjusted by Area: This selection divides the number of hits for each polygon by its area on the map, with the shading reflecting the density of hits. This is particularly useful when comparing results for the large extra-mural parishes of Westminster and Middlesex with those from the small parishes of the City of London.
  • Polygons Adjusted by Area (no border): As with a simple Polygon Adjusted by Area this display format divides your data between polygons divided by area, but does not mark out borders. It is particularly useful when exploring the distribution of densities (of crime or population for example) across space, and should normally be used with a blank base map.
  • Pins adjusted by Area: This will display your hits as pins, but collect them according to type of place you have grouped by (such as parish), with the size of the pin determined by the number of hits divided by area. The relative density of hits will be reflected in the size of the pins displayed.
  • Small Blocks: This display format divides the whole map surface into square blocks and displays the relative density of hits per block. This is particularly useful when using data which includes different types of place names (such as parishes and street names), since every hit is included. Where a place covers more than one block, the hits are divided proportionally into each block. Small Blocks are particularly useful when exploring the geographical distribution of densities for data that is not dependent on parish administration.
  • Large Blocks: This display format divides the whole map surface into larger blocks and displays the density of hits per block. Large Blocks are particularly useful when exploring the geographical distribution of densities for data relating to large regions in London such as when comparing the west end with the east end.

Reading the Colour Density Range

When you map data as polygons it will be displayed as increasingly dense colour blocks, from, for instance, transparent to dark blue. Although the human eye cannot distinguish more than five shades of colour, the results are a continuum of shading. By selecting Disregard This Place from the data balloon accessed by left clicking a polygon, you can eliminate that polygon's data from the calculation used to determine the shading of the map as a whole. This is particularly useful when anomalous results for a few locations make it difficult to distinguish differences on the rest of the map. Using a Blank base map, selected from the upper right hand menu, will make the depth of shading stand out more clearly.

Left Button Functionality

You can access detailed information and more functions by Left Clicking your mouse over any Polygon or Pin. This will bring up a balloon displaying the name of the Place on the map (whether a parish, ward, or street) and the number of records associated with that Place from the data you selected. You also have the option to Show the data. Selecting this option will take you back to the Data page (you can navigate back to the map by clicking on the Map tab in the upper right hand of the page). The balloon may also contain information about how the data have been Grouped. Finally, at the bottom of the balloon you are given the option to Disregard This Place (you may need to use the scroll bar in the balloon). See Reading the Colour Density Range.

Accuracy and Interpretation: Important Health Warning

The value of your results depends entirely on the accuracy of the underlying data. Each dataset has its own limitations concerning the accuracy and thoroughness of the place name information provided, so you should familiarise yourself with the original dataset before drawing any conclusions. See the Historical Background pages for information about each dataset, and links to further information. In addition, the process of geo-coding place name information to enable it to be mapped is subject to a degree of error.

In particular, you should be aware of the following potential sources of error:

  • Were place names regularly provided in the original source? If not, as is the case with defendant homes in Old Bailey trials, the results will be incomplete.
  • Do data survive for all of London? Several parishes are missing, for example, from the Four Shillings in the Pound tax.
  • Were place names in the original text consistently marked up as such in the electronic edition? Place names in London Lives, for example, were mostly tagged using an automated process, which was subject to a degree of error. For more information, see that project's About this Project page.
  • Does the dataset contain a mixture of different types of place name information? Several London Lives document types, such as the Minutes of the Court of Governors of Bridewell, include information about a mixed group of individuals, in this case petty criminals, apprentices and governors. It may be possible to filter out irrelevant data by adding keyword(s) to your search criteria or by using the disregard this place feature discussed above (under Reading the Colour Density Range). Alternatively, you can export the data and edit the results in a spreadsheet.
  • What proportion of the place names in the data have been successfully mapped? As explained on the Geocoder background information page, many place names could not be successfully geo-referenced, because the information is incomplete, ambiguous, or the place name does not appear on contemporary maps. The Data search results pages indicate the proportion of the first 200 results for your search which could be mapped. By clicking on Show more hits you can page through the data to see the success rate for additional groups of 200 hits.

Citing Your Results

If you wish to use a map generated by this website in your research, you need to include a citation which documents the process by which the map was compiled. For advice on this, how to cite material from this website more generally, and see our terms of use, see our Copyright and Citation Guide.