# Geovalidation¶

## Raster strategy¶

This allows **constant-time**, random-access lookup of locality.

**expansion of shapefile boundaries**so they partially overlap, to create fuzzing when a coordinate lies on or near a boundary**coordinates within 5 km of the boundary**should be considered valid if they are in the locality**on***either*side of the boundary- According to Brad, "In the past we have toyed with various buffers up to 10 km. But 5 km sounds good, let's go with that." _
^{2}

- According to Brad, "In the past we have toyed with various buffers up to 10 km. But 5 km sounds good, let's go with that." _
- expansion performed by converting polygon vertices to polar coordinates, increasing the radius coordinate by 5 km, and converting back to rectangular

**cylindrical projection**of spherical Earth onto**2D lat/long rectangle**, for each vector shapefile^{1}- *possible cylindrical projections*:
- *Mercator projection*
- *Lambert cylindrical equal-area projection* (uses a cylinder the same height as the sphere
^{1}) - *equirectangular projection* (y-axis is latitude angle)

- *possible cylindrical projections*:
**rasterization**of projected shapefiles to 5 km pixels- when shapefiles overlap, pixel contains a locality value for both localities

**constant-time**, random-access lookup of locality using**C++-style 2D array**- lat/long mapped directly to x,y array index, allowing direct access without a log(n) sorted array/binary tree lookup

- if exact
**point distance from boundary**is needed, it can be determined separately using the appropriate vector shapefiles for the matched localit(ies)- According to Brad, "we would like to be able to determine error distance for points falling outside the boundary. However, quantifying error is much less important than simply knowing if a point is inside the buffer and can therefore be used in analyses. Perhaps quantifying error could be a background task, after all the observations have been classified as in or out." _
^{2}

- According to Brad, "we would like to be able to determine error distance for points falling outside the boundary. However, quantifying error is much less important than simply knowing if a point is inside the buffer and can therefore be used in analyses. Perhaps quantifying error could be a background task, after all the observations have been classified as in or out." _

^{1} Lambert cylindrical equal-area projection from Wikipedia:

^{2} e-mail from Brad on 2012-10-23