Flag of Saint Vincent and the Grenadines — construction sheet
Own work. This construction sheet is not based on government specifications because there is no evidence that any such such specifications exist.
Instead, this sheet is based off measurements of the primary GIF image at Flags of the World (FOTW). The GIF image was created by Željko Heimer in 2003.  To clarify, the GIF image is not a construction sheet; it is a simple image of the flag without dimensions or labels.
The FOTW GIF image was chosen as a reference image four four reasons:

The image was done by a known and respected vexillologist.
The image has been stable for eighteen years without signs of morphing.
Detailed analysis of the image reveals that it is carefully laid out on an isometric grid with considerable attention to symmetry and detail.  This allows it to be accurately vectorized without introducing changes.
The same image (converted to PNG format) also appears on a prime Government web page: House of Assembly —  History of the Flag. This implies that at least one branch of government has informally accepted it as being a legitimate representation of the flag.
Note: there is a different flag image at Ministry of Foreign Affairs and Foreign Trade — The National Flag. It is a poor quality JPG image that is either cropped or badly drawn; the width of the blue and green rectangles are not equal half the width of the yellow rectangle. It is completely unsuitable to use as a reference flag.
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