![]() ![]() ![]() text strings of different lengths), the user will need to undertake some explicit mapping of fields in order to tell ArcGIS how to combine and present the fields in the output file. Any differences in fields, field names, types and definitions should also be considered prior to merging shapefiles: if the files contain the same fields and the field names, types and definitions are the same in each file (as in Figures 2a and 2b), the merge is likely to be simple and unproblematic, however if they contain different fields or if the same field has different definitions in different files (e.g. merge points with points polygons with polygons. Note that it is only possible to merge shapefiles which contain the same data type i.e. The process of combining shapefiles which overlap geographically is conceptually and practically different and usually better achieved by using tools such as Intercept and Union. Note that merging works best with shapefiles which are adjacent to one another but which do not overlap geographically. This process is known as "merging" within ArcGIS. If the user wishes to map these boundaries and/or join attribute data to them, they can continue to work with the two separate shapefiles, or it may be easier to combine them into one single shapefile. Figure 1c shows the two sets of boundaries mapped together.įigure 1a: Local authority district boundaries within Hampshire 2001įigure 1b: Unitary authority boundaries within Hampshire 2001įigure 1c: Unitary authority and local authority district boundaries mapped together but still as two separate shapefiles A typical example is shown below, where Figure 1a is the shapefile containing the 2001 LAD boundaries in Hampshire whereas Figure 1b is the shapefile containing 2001 UA boundaries that fall within the geographical extent of Hampshire (i.e. A classic example is when working with data at the local authority district (LAD) and unitary authority (UA) level: from many data download services it is often not possible to download one single shapefile containing both sets of boundaries rather, two separate shapefiles must be downloaded, one containing the boundaries for the LADs and one containing the UA boundaries. Sometimes, if the user has obtained shapefiles from different sources, or if they have had to download shapefiles separately for different parts of a study area, they may wish to combine them into one single shapefile for ease of analysis and mapping. ![]()
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