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Add a filter extension to allow filtering individual attributes

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Eric Fischer
2018-06-18 11:26:22 -07:00
parent 54983c7536
commit 8d6bd4e10f
9 changed files with 148 additions and 72 deletions
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@@ -229,9 +229,20 @@ tippecanoe -z5 -o filtered.mbtiles -j '{ "ne_10m_admin_0_countries": [ "all", [
Example: to retain only major TIGER roads at low zoom levels:
```
./tippecanoe -o roads.mbtiles -j '{ "*": [ "any", [ ">=", "$zoom", 11 ], [ "in", "MTFCC", "S1100", "S1200" ] ] }' tl_2015_06001_roads.json
tippecanoe -o roads.mbtiles -j '{ "*": [ "any", [ ">=", "$zoom", 11 ], [ "in", "MTFCC", "S1100", "S1200" ] ] }' tl_2015_06001_roads.json
```
Tippecanoe also accepts expressions of the form `[ "attribute-filter", name, expression ]`, to filter individual feature attributes
instead of entire features. For example, you can exclude the road names at low zoom levels by doing
```
tippecanoe -o roads.mbtiles -j '{ "*": [ "attribute-filter", "FULLNAME", [ ">=", "$zoom", 9 ] ] }' tl_2015_06001_roads.json
```
An `attribute-filter` expression itself is always considered to evaluate to `true` (in other words, to retain the feature instead
of dropping it). If you want to use multiple `attribute-filter` expressions, or to use other expressions to remove features from
the same layer, enclose them in an `all` expression so they will all be evaluated.
### Dropping a fixed fraction of features by zoom level
* `-r` _rate_ or `--drop-rate=`_rate_: Rate at which dots are dropped at zoom levels below basezoom (default 2.5).