Arc4You Data - Hints to join attributes
There are some differences between the normal Spatial Join of ArcView (Join Attributes) and the two new functions
Load Attributes and
Sum Attributes to join attributes from a source to a destination table:
- Dynamic contra static join: The normal Spatial Join of ArcView is dynamically, this means it is updated each time the project is opened. The advantage is that the attributes are always up-to-date and don't consume additional hard disk memory.
The disadvantage is, that it may take a long time to join large tables and it has to be done several times for themes that are used several times in your project. This may slow done the opening of a project considerably.
and Sum Attributes
are static "joins" that are normally only done once, because the fields are added permanently to the table file. After changing the topology of the themes or field values of the source theme the "join" has to be rebuilt again though, if the values should be up-to-date.
Moreover joined fields can neither be edited, modified or deleted! You can use the function
Freeze Fields to make a dynamic join permanent, this means to convert the joined fields into "real" table fields, that can be edited in any way. The freezing of joins speeds up the opening of the project too.
Spatial relationship between features: A major disadvantage of the Spatial Join
is, that the join between lines and polygons is only done when the feature is completely contained in the other feature. As this occurs very rarely, most fields stay empty. This is quite annoying between line themes, because it hardly ever happens that a line is totally part of another line. Actually it only makes sense to join point themes with other themes.
and Sum Attributes
support all joins between source and target themes (all combinations between points, lines and polygons) in a useful way. This means, that only a partial overlap is necessary between lines and polygons (the degree of overlap can be used as a weighting factor in all calculations). A reasonable join between line themes can be created by buffering the source theme.
Number of joined records: With Spatial Join
only a single record from the source theme can be joined to a record of the target theme (even if many records would be matching). With
the attributes of several or all overlapping features can be loaded, because for every single matching record a group of fields is created (like in a pivot table). With
the single values of all overlapping features can be summed up to a final value (this means you can perform complex calculations).
Ranking and weighting of the values: The ranking of the single features with
and their weighting in the calculation with Sum Attributes
is done by the distance to the point, the length of the overlapping line segments or the area of the overlapping polygon. The nearest point, the longest line or the most overlapping polygon is loaded first or weighted highest.
© 2003 WLM Klosterhuber & Partner OEG