| ... | ... | @@ -13,4 +13,9 @@ For our example here, we'll download US States. (It also includes "state equival |
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FYI, [TIGER/Line](https://en.wikipedia.org/wiki/Topologically_Integrated_Geographic_Encoding_and_Referencing) is what the Census Bureau calls their data model. [Shapefile](https://en.wikipedia.org/wiki/Shapefile) is a file format.
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### Step 2. Topology-aware simplification |
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### Step 2. Topology-aware simplification with MapShaper
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You might have noticed the file you downloaded — which is a ZIP archive containing several files (And yes, all of them are part of the "Shapefile"; no, you can't delete everything except the .shp.) — is about 10 MB in size. If you were get ahead of our process and convert it to GeoJSON now, you'd end up with about 6.5 MB gzipped. Ooof.
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Obviously, our little web map doesn't need to be quite this precise enough to see every little bend in every river that forms a state border. Fortunately, just about every GIS tool out there has tools to shrink file sizes by dramatically simplifying shapes. A good and widely available algorithm is Visvalingam’s Algorithm, for which you can find a very nice, visual explanation [here](https://bost.ocks.org/mike/simplify/).
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*Un*fortunately, most of those tools are not topology-aware: they're going to process, for example, the Georgia-Alabama border once for the Georgia shape and once for the Alabama shape, possibly making slightly different decisions for each, leading to small gaps or overlaps. This is where [MapShaper](https://mapshaper.org) comes in. |
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