THE MAP.
The map which accompanies this work is based, as far as my own route is concerned, upon astronomical observations made at the principal places, upon daily observations of the compass, and in regard to localities which 1 have not visited, upon the best authorities in existence. The latitude and longitude of many places in Mexico will be found to differ often widely from their positions on Mexican maps, which lay the latitudes generally too far north; the longitudes too far east.
Being rather poorly provided with astronomical instruments; occupied, besides that, in the most various pursuits, and having no scientific assistance whatever, I had to confine my astronomical observations only to the principal stations. But as on the northern part of my route many points had been already determined by former explorers, and in the southern part I enjoyed the valuable aid of Dr. J. Gregg, (as mentioned in the preface,) sufficient points have been ascertained for the practical purposes of a map, whose principal object is to enable the reader to follow my route and to correct the many gross errors, not only in minutes but even in degrees, that are commonly found in Mexican maps. In connecting my daily sketches, I have laid down the country only as far as it fell under my own observation, leaving to future explorers to ascertain the regions beyond that.
Taken as a whole, therefore, I believe that this map, though by no means as perfect as I wish it to be, will at least be found more correct than any other published at present of the northeastern part of Mexico; and although, on the two end points of my route, that have been explored also by the engineer corps of Generals Wool and Kearny, it will not be able to compete with their more elaborate maps, it may nevertheless deserve some credit for filling up a large intermediate space of nearly 1,000 miles between Santa Fe and Parras, where no engineer of the army has prepared a map of the country, and for connecting, in this way, the scientific labors of the two engineer corps attached to General Wool's and General Kearny's expeditions.
As my own route embraces in substance the long, celebrated march of Colonel Doniphan's regiment, it will afford for that reason additional interest to the public. Besides that, I have laid down the march of General Wool from Corpus Christi to Parras, and General Kearny's from Bent's Fort to Santa Fe, according to the unofficial memoranda of several officers of those corps, (I claim, therefore, no authenticity for them,) and have added all the rest of the most interesting routes that have ever been travelled from the United States and Texas, to New Mexico and Chihuahua.
