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author | isabelle-dr | 2022-03-22 19:33:40 -0400 |
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committer | isabelle-dr | 2022-03-22 19:33:40 -0400 |
commit | 24e89c97cbbdd89348b1f02497a129ac8ac0a14f (patch) | |
tree | ac8432b0731525e889b6dfefa1401ce277af6893 /.idea/gtfs-book/ch-09-shapes.md | |
parent | ab1b75da67be3e101e40e0ae3052d73c714b8ea3 (diff) |
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diff --git a/.idea/gtfs-book/ch-09-shapes.md b/.idea/gtfs-book/ch-09-shapes.md deleted file mode 100644 index bc05636..0000000 --- a/.idea/gtfs-book/ch-09-shapes.md +++ /dev/null @@ -1,76 +0,0 @@ -## 9. Trip Shapes (shapes.txt) - -*This file is ***optional*** in a GTFS feed.* - -Each trip in `trips.txt` can have a shape associated with it. The -shapes.txt file defines the points that make up an individual shape in -order to plot a trip on a map. Two or more records in `shapes.txt` -with the same `shape_id` value define a shape. - -The amount of data stored in this file can be quite large. In -*Optimizing Shapes* there are some strategies to efficiently -reduce the amount of shape data. - -| Field | Required? | Description | -| :----- | :-------- | :---------- | -| `shape_id` | Required | An ID to uniquely identify a shape. Every point for a shape contains the same value. | -| `shape_pt_lat` | Required | The latitude for a given point in the range of `-90` to `90`. | -| `shape_pt_lon` | Required | The longitude for a given point in the range of `-180` to `180`. | -| `shape_pt_sequence` | Required | A non-negative number that defines the ordering for points in a shape. A value must not be repeated within a single shape. | -| `shape_dist_traveled` | Optional | This value represents how far along a shape a particular point exists. This is a distance in a unit such as feet or kilometers. This unit must be the same as that used in `stop_times.txt`. | - -### Sample Data - -The following table shows a portion of a shape from the TriMet GTFS -feed. It is a portion of the shape that corresponds to the sample data -in the `stop_times.txt` section. - -| `shape_id` | `shape_pt_lat` | `shape_pt_lon` | `shape_pt_sequence` | `shape_dist_traveled` | -| :--------- | :------------- | :------------- | :------------------ | :-------------------- | -| 185328 | 45.52291 | -122.677372 | 1 | 0.0 | -| 185328 | 45.522921 | -122.67737 | 2 | 3.7 | -| 185328 | 45.522991 | -122.677432 | 3 | 34.0 | -| 185328 | 45.522992 | -122.677246 | 4 | 81.5 | -| 185328 | 45.523002 | -122.676567 | 5 | 255.7 | -| 185328 | 45.523004 | -122.676486 | 6 | 276.4 | -| 185328 | 45.523007 | -122.676386 | 7 | 302.0 | -| 185328 | 45.523024 | -122.675386 | 8 | 558.4 | -| 185328 | 45.522962 | -122.67538 | 9 | 581.0 | - -In this sample data, the `shape_dist_traveled` is listed in feet. -There is no way to specify in a GTFS feed which units are used for this -column -- it could be feet, miles, meters, kilometers. In actual fact, -it does not really matter, just as long as the units are the same as in -`stop_times.txt`. - -If you need to present a distance to your users (such as how far you -need to travel on a bus), you can calculate it instead by adding up the -distance between each point and formatting it based on the user's -locale settings. - -### Point Sequences - -In most GTFS feeds the `shape_pt_sequence` value starts at 1 and -increments by 1 for every subsequent point. Additionally, points are -typically listed in order of their sequence. - -You should not rely on these two statements though, as this is not a -requirement of GTFS. Many transit agencies have automated systems that -export their GTFS from a separate system, which can sometimes result in -an unpredictable output format. - -For instance, a trip that has stop times listed with the sequences `1`, `2`, -`9`, `18`, `7`, `3` is perfectly valid. - -### Distance Travelled - -The `shape_dist_traveled` column is used so you can programmatically -determine how much of a shape to draw when showing a map to users of -your web site or app. If you use techniques in *Optimizing Shapes* -to reduce the file size of shape data, then it becomes difficult to -use this value. - -Alternatively, you can calculate portions of shapes by determining which -point in a shape travels closest to the start and finish points of a -trip. - |